In what ways is the word “work” as used in everyday language the same a hbkeo i 2v.1bhikr1e8n3nm. +s that defined in physics? In what ways is it different? Give examples ofk1 1i.en+ vrnkmob2h 8h3 i.be both.

Can a centripetal force evg)4o cciyw2l6hixtisz7i20 k2 w5wrd s em()5er do work on an object? Explain.

Can the normal force on an 0-nazu3yez k2object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she oe-tyu-0g)r epti5,rm * d-oydoing any work? If rm,gp * - -t-0o)yeuid tryo5eshe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negatiwmj+6b3 g4 nsjve? [Hint: Consider what happens to the dishes when mb+n3jj w6sg4you pull a tablecloth out from under them.]

Why is it tiring to push hard against a soli cw6:-liepw d)d wall even though you are doing no workc:ide wplw)6- ?

You have two springs that are identical except that spring l is stifff(3rr+ qcl+pher than spring pf+rrcl+q (h32 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant hor87g b6e-re 93vbnpwi tizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoi9vn 836 t-rw epig7bbent A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change r, 56dd8tltk-)+ht bp: narj jwhen you jump as high as you ca jd6t +:-k ljr,5)ab8dthrtpnn?

In Fig. 6–31, water balloons are tossed+c ty 6;u j3(fgbt(kwm from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ig(m 6jb3tut gw(yc+k; fnore air resistance.

A pendulum is launched from a pointal o.b 3lb8 (hlue5;dn that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the traan bbd ;3 e.uhll85o(ljectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring bgp,w9kpit a0 + :juf7jy pressing down with your hand and then release it, can the spring leave the table? Explain, usf ,7pwiaj 0utkjpg:+9ing the law of conservation of energy.

A bowling ball is hung: tg1*q(m/ qb0jjonvy from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against hojv y( qjbg*q: 01m/ntis nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when wa .h/zlvdqsj )q/ s3:rddc2hylrxh2e)t6 .q c,ter at the top of a waterfall falls to the pool h/ts l r.z6hd cscx)2q)r/qd . ,:vey 3hlq2djbelow?

Describe the energy transformations when a l05dlb/ v)n vn2krpm .child hops around on a pogo stick.

Describe the energy transformations thatr,zykqt yoo, +xv p8l09v :f5x take place when a skier starts skiing down a hill, but after :q xf50zy8tvlo 9,ovp,kxr+ya time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts mkl4rjh-/sq0from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend o4j 0ms-qlkh/ rn the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers preferm11 1 z6wnjxu k,w9:wkp* bqdc to step over a fallen log in their path rather than stepping on top and jumping down on the other side. qw ,j9x*m1w6 uknpdbwk c1 z1:Explain.

Two identical arrows, one with twice the speed of the zj.d d w,2 +;4kimozab3fe:ksother, are fired into a bale of hay. Assumin4: i+sz;b o e2ka3dw,jzfdkm.g the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energyl8gp)208cfi (o6 sm-n 4cbier lby wu+, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to b-rpw oe gfibyc86+l04m (l)c2b8u nise wound up.

When a “superball” is - ebng /;+cp -pr m.iwlw,gc7:) djbzfdropped, can it rebound to a height greater than its original height? p)+w:pic mg nd.7cw-b gl zf;ejr,/-bExplain.

Suppose you lift a suitcase from the floor to a table. The work you dozd+ym.tf +1 iy on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) th yt+.1dz+ymfi e weight of the suitcase?

Repeat Question 22 for the po8gk9sui wbj 1/wer needed rather than the work.

Why is it easier to climb a mounta ogq3o)japdbg , g 7gg2/l4,xwin via a zigzag trail than to climb straight upp32 ag,ogl)w7b o4g dq, g/gjx?

Recall from Chapter 4, Example 4–14, tha1*3yuswyx (r+8a x* k xxvpj)rt you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? v81y y)x3 *rkxajxx+r*w( psuAccount for this, using energy concepts.

  How much work is done by the gravitational force wheqgb s*: fl7wvajw5j*8n a 265-kg pile driver falls 2.80 m?g w*f8:ba5 7j*sqvljw    J

  A 65.0-kg firefighter climbs a flight of ku/ y7qt,k cjj2x56iestairs 20.0 m high. How much work is requi7qt kuyc jije,k6/52x red?    J

  A 1300-N crate rests on the floor. How much work is required to move it at coam:qh+t0te/ g, o wus 4a) 7;xbwv4jmcnstant speedjsmtb0+e4u, w ;ocma74x)qgha /tw :v (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 8nagdv87gc a0;y: ji e160-kg crate 10.3 m across a rough floor wc:vid; 8 j7ayega08gn ithout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fle v+/7b sekx q/gyl:zqy;-t;ywds7a8oor at a rate of for 7.0 dwglt/+ :;7sve/8 y-a e7kszqyqxb;y s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat9mp2ofi, l8fsnnys+.y .fjq / on a table. How much work is required to stack them ony. m+ yfsjffni892 q .n,ps/loe on top of another?    J

A lever such as that shown in Fig. 6gw*h vf3u)uo 4,skbl2cbh/f;3 t e3o e-35 can be used to liff objects we might not otherwise be able to liff. Showo 3 gff b s3)4bcoehh vu,;u3e/wt2l*k that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelerating bzc j9is.lpws -a xd09*y a man who is pushing d*piw -j xslc9a09.sz back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to0;tw* 9rzvp)nxi.uzt give a helicopter of mass M an acceleration of 0.9i. )0 upwrtxzn;tz*v 10 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear:j g: tn.+5 tv e90;-cpbehdbn wcs+nb and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x zjm*n 9 ut9:o5ew -xojaxis, varies as shown in Fig. 6–37. Dete-9zet no9uj*mjxow 5:rmine the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle act a4lhz .n4j*698 h+dqdnn * u0qomacogs in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule,u gd9mxw)b )7 8c/ats,tro1qw with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed increase g9h.ug undifrdafc6 /i; +:9cd? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required49amknb;g 0 ft to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tran+: -jv73oy vp/ qpyofveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose st2qw)3ffd 93,c ul v/yulxf )lsring exerts an average force of 110 N on the arrow over a distance of 78 vl y3uf2/s d l)qx f)uf,wc39lcm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm ttckar+* .*q 04mob8ul (dq ,v0kefmo/x xcp0when the balx o+*al,rf8m0m0u( cxqc.qo* vtt /de4kpk 0bl is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car iszb44x-sda5w 0:ilo-f,fw f sv increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s 054sf,-- 4wzsobfiv :l a fwdxreaction time.

  At an accident scene on a level road, investigators measukvbgp6ce0- 2 ure a car’s skid mark to be 88 m long. The accident occurred on a rainy day,0kevcpu6 - gb2 and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pz9:nmp8s de)n itched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the avesdp :n)z n89merage force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kc2rtrew2 c t(2g rock go if thrown straight up by someone who does 80.0 Jr2t 2ctc(ewr 2 of work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single w,+jo8v qjh 6gcable. g+,qjovj h86w Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constargb *eh;5u ve.nt, k, of 440N/m How much must this spring be stretched to store 25 J of p*.bge;hu e5vr otential energy?    m

  A 7.0-kg monkey swings from one branch s, cf6dwh1lu 7/)it ygi6sf;l to another 1.2 m higher. What is the change in potenifd;6)/t,ussh7ig cfl w y1l6tial energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chp1k3zez9qb8a7 v8n ij ange if np i19 ezkz 8bja387qvhis center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h wh a7v 0ey zgouz6:89t5r .v,r9mntwmrgen it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the sprirrtmge9:raw tumz9yv n.,8zvo5 07 g 6ng stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so:83wty,2l hugiln c* w1t,bbl it is 2.20 m above the ground. lbh,ly:u ,2wbltwi1*ct38 g nWhat is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevyf;e0o)9vd pjation of 1600 m and climbs to the top of a 3300-m pea)fe 9 0oj;pvdyk.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m ha0 wx 1pj28m nw/krxoio,v kr(,ngs vertically next to a ruler. The end of the spring is next to the 15-cm mark on th/ k0vnpxio x ,(r m,2jowwk18re ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top sp+ k;cfacyw f7 5z)h9akeed (5.3m/s) and grabs a vine hanging ver5a79wc+c;hfazyfk ) ktically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frib 56sv5d*oukhctionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionlespp/ t(yt n;ba6s 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational z0k7 s 9xmalqr.8m1g )sg: gowpotential energy without the aid of a pole. With wha8sa7g mkmzg1wx0 .l:o9r)qsgt minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top z53f8h* jtzzpof a platform with a speeth* p f3z5jzz8d of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass),ms :wt/ t)lwh7 whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 ml7 tmhs/ :wtw). (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped tr p08n3:pe.:m+p nnxon yneu,nack shown in Fig. 6–39. If the block is to remain on the track, even at p3xn mn0 epnn:p:+nn.,e u 8yothe top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the eero70;hithecim0l.jpsgxa,/gt bvo4 / 1a77 nd of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial m,7g0o7.iex va ls;t// 40ohti1 r gbecjh7padisplacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumpsm6ek -sziy4.k from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’skkz-ym 46e. is law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged urb5nb29 5zso8,lj h dup to point 1 where it is released from rest. Assuming no friction2o5unlz8 h bbs9,d5 rj, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spen 6w ;6t q+ cenmvfbqo:io;9/bed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designiunu3 1b3gdt j *dg(e8mg,e 3csf3mls2ng a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the tmdecgjs 3dt g3u32n(b3e g8us*m1 ,flop of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle ui2id a /k xl8jm.lx3k9p a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 : .l2;u vflbp:rf 7g,-kv xuiikg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy isvrxuv:- bip7. u:;ffki2, gll produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 motq.iz6lpozgw o.y 5 179u;ak 9d nfi* high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to frictiog*fop5lzuz;.9ydnk.7a9o i1 o tiq6 wn was generated in this process?    J

  A ski starts from rest and slilo7 yszovhn4e :86yf-w0 b5nep57oyza g.g l 2des down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m abobb dv8lvl .2vua3r.c4 ve the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces b4gzv-f fa 1;4i.duuc wack to a height of 1.5 m. 4uvz 4iga f-cdw;1u .f
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a flooc476f) +gaag0brv8nj)qusi e k1z g7nr with a constant horizontal force of 350 N. For the first 15 m the floor if)gne47snr ggjv 6kb87+zaui0 1qac) s frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of Ifdyfb7 h6:vx6 z;5 dchd the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance tr ; hc6vd6h7:zdyx dfb5aveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachesoezu va-e b4lm.3:o4i(j f2gb the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block iyq;+k2zk h0n -1j2n.w wix4aodqumu m9 r vf5,s firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and t .0zi2xk,qqajr;5n9vnm -21f4dw w ku m+yhou urning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly am;v;8d i2mg 6vw6riy)z vri2tz la3f0ttached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30dr ig;vta;zzr 0f6ywm 3vm6i l2 8)i2v. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used*2eev8 )55fdai * vreel)mirjumh ,)t a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually lan2 mhjl))5d i et5a)e** vu,8efvemrrided at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-.ko:n,.ds bf/up5ni l0ujy ;qstory window 16.0 m above? bs,n.nlq.5op :j yiuu/k;df0    s

  If a car generates 18 hp when traveling at a steady 88km/h wibj. wn 0-4ez) aybq,vhat must be the average force exerted on the c-j4)bw iy ,0evqanb z.ar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from px/.6zxls.zu rest to 95km/h in 7.4 s. What is the average power delivered by the e./xpz x6 ulz.sngine?$\approx$    hp

  (a) Show that one British 00ii3im unyjo( s ikqc1 m/ok6ts /l2(horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in thfxqw;4q+u9h re form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.z:i7uiegkj azb79 io2u3iz,b7d( d 7f0 s on the level when it is in neutral. Approximately what power (watts and hp) is neededukii7,d(73j:f igi z b7eazu2 d 7z9ob to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do inlhq bfn9* 9cwnd7j99ba4x/ ev 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kgv:b .-cx 8+r 7vtjlf; v3kxssy shot from rest to 14m/s If this motion takes 1.5 s, w3vv x+:sxcj f7r-by v8.l; stkhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heightq uw i587h p7.(7z)wvr stpgklz9g8fz of 3.60 m. What output rating (watts) should the pump motorts 7z9qu8wkrpp 77 iv (lhf8gzgw5 z). have?    W

  During a workout, the football players at State U. ran up q:my dw 03) s sda)v3vcvnli29the stadium stairs in 66 s. The stairs are 140 m long and inclism d ylind9qcv3sa2w:0) )v3v ned at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist y .;gxj9 hju-yjj4.e,ls,cx6mf i7vf climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum powe5 hqj dfl5-w7lr output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h5dwqflh-jl 57 if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must /kqeb pl0o2f.x 8wd,i a motor have to be able to drag a 310-kg box along a level flo,0d bkwi2/ p.8lq eoxfor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downbpq iv1 j)/z65i3def9 tp dj)v a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are desi;hv 55 (btjts*sk( ;xdej,js agned to compress and rebk ; (*hsx( dve;tb55,sjsjajtound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0zy8l0q3o.-hr n3hsz o cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the bly zs3 0o.-o 3rqzhhn8ooks are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous lonh4n gki0fr: zo5 * a/dh6tw1+vs v:/h e-inihig jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch4iwniti1 0*n hs hr+-avid g 6ehvo5/ f::z/kh if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the ls jlmwrg (v92-ooped track shown in Fig. lgjws v- 2m9r(6–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hisag vb u .e 8o0bcc(bl:kr0as+, parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuri0+bbar.kgsbc:(oe80va u l c,es. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of lesrv dne,;xq8r4-- q gnngth L whose other end is fixed (Fig.vrxq-q n, n84rse;d- g 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is madnx05z pht8-l*s *r sxm)tio* 7)dlzwie in 5.0 h starting at an elevat*izs 5p * oll)xntmrzx*s0td7)hi-8 w ion of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 92c wdb w53yw9j/bw6e;z 0-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,qyj:7)3eco- v. riivw 000 people per hour. If v.r-: q)oiweiyc 3jv7the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 y;82ucxvln8bup: n/i m before stu ibl8 y /c8up:nv2n;xriking the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster 176 lcl)em:4xy 0vi fglsje.gwith a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop anl ym)eigfx l046:vcl.7es gj1d the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bs k;anv4 g e + kti:5,-v-f7k2 qvgdwe0wc:nxaar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one barg+c:7gnq 45,vk-dw s; f-eatvk0 an:kwxiv2e (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45p8f:tkr8dym lhg9 e35 .0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, t6qo +/tcj0q2m/su p sihe spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if youqmc/s/ 0q j6o2 upit+s jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings outqfz71t;j pg8(t+ kisu over a lake (Fig. 6–45). He releases+ gptj87 ifk;(q1z uts the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical- xxsm :4l9tuv distance of 5.0 m in 9.0 s. What minimum powe:ts9xl4-v mxur output was used to accomplish this feat?    W

  Some electric-power companies use water to stjbd kh*m4:* qnore energy. Water is pumped by reversible turbn*m* dh bkj:4qine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k y;kdrudc9/ *zy 74won8qjd+g is cut in half. What is the spring stiffness coy; /ojr gz 94wnk+uq*8 d7ddycnstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8: qzl+- y;wnab.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can (etvq01jr( ar accelerate from 35km/h to 55km/h in 3.2 s, how long will it take to acceleraa1( tve qrr0(jte from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cmvhy9 luij.k.2 1ff q5ardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimatvlhu9mf j5ky.fi.q1 2e the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanwm5v pv9nlz 49tc9l ,fce of 500 m, what was its velocpvf n9m9zt4 w 9vl5l,city when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a heicb qz.e6 4;e6lw( uc2jkum*gjght of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its mau.6jzg6bc e2ewm k; 4q*u cl(jximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s