In what ways is the word “work” as yspk- nffcfpk8fo.1.a75 jt l7(1 vc lused in everyday language the same as that defined in physics? In5f1kn1tf ac(kc op f..j p-8slf77ylv what ways is it different? Give examples of both.

Can a centripetal force ever do :.f9exg ,y ssz)bk0 nhwork on an object? Explain.

Can the normal force on an object ever do work? Explainars(f 4bp 2.zam b.j1r.

A woman swimming upstream is not moving with respect to the shore. Is 2 pe sw t5v)a*jgzd34jhh)y dn0)b3 ghshe doing any work? If she stops swimming and merely floats, is work done on) v2e*)ph a3t 0dj )yn5g 4gdjswb3hzh her?

Is the work done by kinetic friction forces always negative? l)twv.ew x; 2f[Hint: Consider what happens to the dishel2wt ve. f;wx)s when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even thp6h+i q*u p9xqough you are doing no worku + ipp9*xqq6h?

You have two springs that are identical except that sprinfqt6q0 k.zkrm*jtczft+ , *fb31i qn;g l is stiffer than sprintz3k rtb0itqmq .z knqf f* +fc6;j*,1g 2 $(k_1>k_2).$ 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 horizontal force on a*3p grxeh: 0ea block that is free to slide on a frict3e0:prhx*g eaionless surface (Fig.6-30). The block starts from rest at þoint 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 doestxhh sem4mt0x4+ cadzzmr5+s4 j42a * your gravitational potential energy change when you jump as hmhtc 4rej02mms da 5xx4z+zsa*+t44high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wpg 4+w8mh, jf2urejv /ith the same speed but with different launch angles. Which one has the highest sp/8+gmhjjr2efpwv 4u, eed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height (/v ibm rqf4g3ib8u;b t iz1b4h above its lowest point in two different ways (Fig. 6–32). During both launches, the penduf;gzm b(qi3v/tu4 4 bi1b8rib lum 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 trajectory. 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 tablq, ajo96ja+d3 hubt2vx * t8ge tb-d1de. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law o1d-8jttbjaxb2*gde3 9+oa tdh6 uv,qf conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inst(cv * z.yoa4s)k z,pwn0eno 6;; zwlhiructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the b)k ws 4(oyn.havwznzi,cl*z6 0o; ;ep all without pushing it. Why?

What happens to the gravitational potential energy when water at the top2 rm .c3 cjd3*)bw)nyoj82iy:tvw mgf of a waterfall b)cfj33omy:wg2m 2)*n 8.ycr dvtjwi falls to the pool below?

Describe the energy transformations when a child hops around on a pogo stick.kcvn732 .uwoyr ce c85

Describe the energy transformations that take place when a skier starts skiing dtpo bic4gk,1ef4 q50i own a hill, but after a tik15i40 qc otb,iep 4fgme is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill ofvsy8 d) u8ukq3 2nng(l height h and slides down. Does the velocity at the bottom depend on the angle of the hq (8nys8unv3dk2 gul )ill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather thaklog*cg ) ak ,zj2lar68 7le5xn stepping on top and jumping down on the other side. Explain*)5 6eagzxl8 llgr2, ojk7kac.

Two identical arrows, one with twice the speed of the other, are firedv6c xg.cjm1l g m jtr2*r4mk)2 into a bale of hay. Assuv4g ljmmrctr2k6cm* x 1)g j.2ming 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 energ br5d q:3ikbx 1k)bm6ty, (a) ignoring friction, and (b) taking friction into account. Explain why a gr6b5mk1bkd) t qxbr3 :iandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its orig d .ae8w3ioh9.a pa2 *2lao(k6xfqv yginal ha w2x2 *k3 ilhg.69ayado(va oq8p fe.eight? Explain.

Suppose you lift a suitcase from the floor to a xblfqdk2/y5ufu fx2- ty t*7,table. The work you do on the suitcase depends on which of the following: (a) whether you lt*ku fx du/y ,f5bf7ty22-qx lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the worr8s oftft+w a5v34j7ak.

Why is it easier to climb a mountain via a zigzz5t.sc5os sobt 57p:v ag trail than to climb straight uo ps.5:57to5 sst bvczp?

Recall from Chapter 4*y(w u:arxtkyu3pt ;), Example 4–14, that 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 raise 3(*atk wu ytp:u)r;xyd, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile dr7 iwwcjrx3s1 n54 i+ennb f0*civer falls 2.8ici5 +*1 n0wn jfe4 3xnbrcs7w0 m?    J

  A 65.0-kg firefighter climbs a fliyii2 y4nq pd3tu-);fe ght of stairs 20.0 m high. How much work is requeyp3-;4uid 2ifqn ) tyired?    J

  A 1300-N crate rests on the flooriu ;vb(/g5va d. How much work is required to move it at constant/gv5d (au;ivb speed (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 160-kg c3r ;rm+u3b 8fbvi/n awrate 10.3 m acromiw/a u ;bf83rvr+3bn ss a rough floor without 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 floor at a rate of w33bxv+*mw 1 rtxkp c; for 7.0 s. Find the net work donmvw*+1x ; bwcxr33kpt e on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, l8m4 sjm-( t,xar0dc8i4 zj ewqie flat on a table. How much work is required to stack them one on top of anoth mie(8s rc4d80,-4w ajtqjmxz er?    J

A lever such as that shown in Fig. 6-35 can be used to lfeluth(h/s 9.r6wur u4qjy9 9iff objects we might not otherwise be able to liff. Show that the ratio of r juh/thelsu9(wrf q. y 99u46output 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 keppoev r-g30w3et from accelerating by a man who is pushing back on it pagwe 3v-oer3p 0rallel 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 requir(oz-nuth z* 9:b6xbx zed to give a helicopter of mass M an acceleration of 0.10 g upwn-xhb 6t*zz(: buzo x9ard.    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 y*vj r90s :h,h mdb4pyand 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 axis, varies as shown in Fig. he v05ww lujj6eo7x: ;6–37. Determine the work done by w5l owj6he7j0 v;xeu :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 v8b a a9spdk*avlj uv:i*m92p 0q*/gga particle acts 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 oxfnlww+oz z/6i 6:l1ahygen molecule, 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 speehcgw/0v qq 3j*i0kb3 pd increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop aok2 2lbl7vem0n 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 traveling at 16r arp ympl78505km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average forc6+eo+joh vg .tz/;wi ke of 110 N on ti/k ovto+6g.;zwjhe + he arrow over a distance of 78 cm. 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 25dk9 ,/nbqwby 9w(-mtb cm when the ball is caught. What was the average force exerted by the ball on the glomb( /,nbykqtd 9w -9wbve?    N

If the speed of a car is pd v+d01 ii4adincreased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the drivervdd04di p1 i+a’s reaction time.

  At an accident scene on a level road, i8.elr, zs klt0nvestigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of le. tk8rls0z,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 pitched at By the time it reaches the dc9n o -l1c5ksplate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is ab5-nldc9ko c1sout 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 8buph7 srpeeya.w f; m.,*: )/lj8sywe0.0 J of work on it? Nj.wby 8y s/u :ep p.smr,)*h;lw a7eefeglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration byg57nt*cqixj5 0m (u)ge3jqg t a single cable t5jgx5qg ic*q n)m37(0jutge . 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 43ids+q-bbslk ( b1xoconstant, k, of 440N/m How much must this spring be stretched to st+-bdbqo isxk34 b1 l(sore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to antiw- mtuz yr12c7a i+6other 1.2 m higher. What is the change in potential energy? ac+6mw it1-irt7yz2u    J

  By how much does the gravitati,ka r(tg38v sywuw (v.onal potential energy of a 64-kg pole vaulter change if hi, wvrs 8k(wtg 3vyau(.s 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 when it strir d,mpqp98wn9 kes a horizprw n98p9qm, dontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person 2d+g.ajigi sy9: zg j uao3d6+r1nq 0hlifts a 2.10-kg book from the ground so it is 2.20 m above tjhdja3agg 6 g+ +9 .yus10iinr:qz2odhe ground. What 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 elevatimwd t6iqtc*is5-+z 0fon of 1600 m and climbs to the top of a 3300-m iqd *5t6si-zmcf0tw+ peak.
(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 hangs vertically next to a ruler. The end of the spring 1u//ngof0n xg+pt lgb6ir;z ) is next to the 15-cm mark on the ruler. If a 2.5-kg mass ir1 g6)lxf onnzuggbp/;/ti0 +s 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 speed (5.3m/s) and grabs a 2cn;; qnn1ppc*byrqd6 2hh 6ovine hanging vertically from a tall trrq6bhnh2cy dp;2ocnp* 6 q;1 nee 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, startinzzar16jx + qb /b,98 hrkvwy4dg from rest, slides down a frictionless 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 ay*s6h0m - epwrucu;v0 frictionless 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 gravitati 499pu lb59(ghwagrn r.:oiq oonal potential energy without the aid of a pole. With what 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 o 9rr: nig(qop45a .bhulwo99gf 0.7m/s.    m/s

  A 65-kg trampoline artist j h s4xe,i;l)/pg,uk e4f:pfqrumps vertically upward from the top of a platform with a speed of 5.0 ph ;f eg44,is/e u:)fqlpxrk,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 madr4l ys9,*clb+r)yjq ss), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed cacll9dy4s)b* r, r+j yqn 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 t;du zh;1clt z k4: 4gb ydcw:b*:v)rograck shown in Fig. 6–39. Iu*hdt;g ;z:bw:yz 4bglo:)d4cr1vkc f the block is to remain on the track, even at the 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 end of a spring (sprinb-c v calm)f0lf94 gk(lpl 6.hg stiffness constant k), Fig. 6–40. The block isb l6lp.lvcmcfg(09 af4l) - hk given an initial displacement $x_0$ 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 jumpe7b0m k ,ep(wogr jumps 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 stwb gpe ,k7m(0oiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car showkhf5y1ttxqaf7 ,c1j/vp : +ea n in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at ptxfc/ 7jh5kv1ae1q :p+, atyfoints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a.u spa/dba9 p+e1xcwj 7z,u/tc*r p 5i speed 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 designing a spring to be placed at the bottom o:hd6m4 sz s rs18m,zs+lfi5vbf an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, c14m 8 dbs5fhsz6+lv:,srmsiz alculate 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 up a 7.8g3 63x6h ehbymjr(6bh $^{\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;.g5rr zci,pm*5 gbh q 7650 kg and traveling 95km/h in opposite directions, collide heahr z*g 5mgi;,crp. b5qd-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wit+0zpyd2/i003 z*hhxwwj j qjuh a speed of 2.2m/s3 h0w+ xu0ijz2pj *wh ydjz/0q How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest an;pnfnu0 ;)f1izqg x6wvz.eb9,f; rys d slides 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 .v,nchv7 ,osbt2 ri b;dropped from a tree 13.0 m above 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 back to a heigpess0y6s8, euht of 1.5 m. 80ye eus6s,sp
(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, -c gatf0ri2o7 is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30.co rag-ft 7i02 What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with+e h.ppa*gyrm1pj3* c a speed of If the aver1* gaprh3 c.ye* mjpp+age force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady,l02j78 f-k -iucrtb)bz egiu 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 is firmly attached to a very light horizo;wz1, d-af lfsntal spring (k=180N/m) as shown in Fig. 6 w-ffz1ld;s,a –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 turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spr;qsi cf; zvq9 z*frr 5p/z36je+rjlb+ ing, Fig. 6–40. The block can slide along a table where the coefficient of friction isr;bzvl;/s5 jj + fizrzc+r qq93e*6 pf 0.30. 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 shuttli*bnj/ch;-g3 qe/kbme used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The gliderh *bb-nj/mqi/g3 c; ke eventually landed 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-n;wk- 4).(qnmi1n fxzueu qg6 W motor to lift a 315-kg piano to a sixth-story windoufq16i .w4k(nq) e z-xnn; umgw 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h wha 9p,9bhlr ug+kt must be the average force exerted on the car drhbk lu9,+ 9pgue to friction and air resistance?    N

  A 1400-kg sports car ac- , o:0se mjvoe3prb4bcelerates from rest to 95km/h in 7.4 s. What is the average power delsr-bveo:jp bmo0 , 4e3ivered by the engine?$\approx$    hp

  (a) Show that one British horseuqetk06:i./ yv+xix upower$ \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 da: 2q rb hhi8ik8*zd(often expressed in the 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 he a8)g9y4qytf 0aq2upzr 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keepgqfaqu y09 zy4)82atp the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mottv xyewyv8n7 ;/5nr 7cor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If7+;u ;i7kb :vky zkis4q*om8)vcqz ha this motion takes 1.5 s, what average power was c*kvv:8)74yom k;b zazu;kqhi q7si+ developed?$\approx$    W

  A pump is to lift 18.0 k:9qyg .wnmfs* g of water per minute through a height of 3.60 m. What output rating (waf *s.ym: 9qnwgtts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium staihs(kihi az vi)*3d8 a5rs in 6ki3s8 ha(ivdh*ai)5 z6 s. The stairs are 140 m long and inclined 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 c 2ib11i.kpv5xm cx zp.limb 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 power output of 120 hp. How steep a hioa ma)/cgmkh xl9 g)f3lyj64 9ll can it climb at a con3jcma/4l9g 9hg )6lfyma )kx ostant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dras56j*nj,/inc5l v6 gazk;p jcmn* w+h g a 310-kg box along a level floor atk /wpvjinnlna+m6j5c *hs5 ; zj,g c*6 a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down :.r *b38dlbldgq voz 4u3m.s pa 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/+webvd- 4g+q lh(8km/h) bumpers” that are designed to compress and rebound 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 i wvq 4+b-edl+gnto a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ggs );rj w;2y1s+zxhsaround, 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 baw2;s hy)rszg;1 j xs+ooks, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics shows dh;,mdhr4jiofz6 guzn,/ c2 6 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 launch if he was traveling at 6.5m/s at the top oj 6hzio4nc,d dzu6hg,/mf ; 2rf the arc?   m/s

  The block of mass m sliding wytb0 u e8hx,:vithout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of y0xev u:b,8htradius 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 a5b ewc, ix0.erircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m ber.xc5iew ,0/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 len2q 1uqjx7k4da gth L whose other end is fixed (Fig. x71q4qja 2 dku6–43).
(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 th3(ejnm lv*7a)ep (tji7o s4c de top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation oi vd(3me4a l j(7es*n7pt)co jf 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 6cu wbqk:*kcl+*v9i d,zx7.;uzhunz a 920-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+ +tks6h7kft 6xqbjmgrzn4y gsv..07 can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimat04xgkhr ..j 6 t+qzs+ybn7ft7mvk6 s ge the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam q8iq ban8t2-u at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculq-qti b8 28anuate
(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 with a circular vertical loop (Fig. 6–4e o.if xb)xie75w1ank+x oe,54), the difference in your apparent weight at the top of the circular loop and 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, this5 x5x iien +efw)oabeo .,k17x 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 bar directly into work, how hitqhgin n3:n -sfn*1x:- fo2urgh could an 82-kg man climb a ladder if he were fueled by one bar (=1000kgfu nt 1nhfo2::i3 *nsnrx-q -J)    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 angk80yp yxgwj:ue +wwg0v,2 (ohle of 45.0$^{\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, tfyheb7ys *vh 0 de(w6 2m2pg0hhe spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at it0 h 6myy7h*(2 e wdgb2ehp0fvss peak?    N

  A 65-kg student runs at 5m/s grabs a rope, ap:y6irm u4p4(wo4 b vn6a(sutnd swings out over a lake (Fig. 6–45). He releases the rope when his velocity i46v:t bimu uro (spay 6(4w4pns 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 athljfylh*d3)q26f+yawn 9a k9 u6 zel7 eoete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power knl 6 39a6ew)2+7lu zheyf*aq jf9yodoutput was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by revev rvoo s9 *pv(e86+p6mylc63 s1,spu dh*bfujrc6ulp*hvv8bs+,jfy6 r9 * pm 3v(e1ssu po od6sible turbine 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 is cut in half. What is the spring stioe;d 8ljcw,hkn*r ,pkss7y 83 ffness constant for each o 3ssjck 7y,preowdl h,kn88 ;*f the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3i:nl m6egx;:p7 $^{\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 accelerate from 35km/h to 55km/h in 3.2 s, how lona4jr6vbh3 y8p j+)w sog will it take to accelerate from 55km/h to 75kyhw8+)r36b so4p ajvjm/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stx a+m,c4 ss .npa*zt,sress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-as ,zt.nc ,4m ssxpa*+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 distance of 500 m, whomh .-ur*ix3jat was it ix* ou3-mjhr.s velocity 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 /ivt893qzvxmd *phb* a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricityv dzb/tv q3mi98xp**h output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s