[填空题]
In the design of a rapid transit system, it is necyp, ic/xc0g6szi -2 c0rfxl;g essary to balance the avsm0ki6iy , g ot5o4xnd-3 c:cberage speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea om-nxg3y0i5 itc4o :oskcb6d ,f this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends); min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s. min
