Phy car - Ans.fyi 參考答案

Phy car

2012-10-04 6:37 am

A car comes to a bridge during a storm and finds the bridge washed out. The
driver must get to the other side, so he decides to try leaping it with his car. The
side the car is on is 20.7m above the river, while the opposite side is a mere
2.3m above the river. The river itself is a raging torrent 59.0m wide.

1. How fast should the car be traveling just as it leaves the cliff in order just to
clear the river and land safely on the opposite side?

?m/s

2. What is the speed of the car just before it lands safely on the other side?

?m/s

回答 (1)

天同

2012-10-04 7:37 am

✔ 最佳答案

1. Let v be the speed of the car
In the horizontal motion: 59 = v.t
where t is the time of flight
hence, t = 59/v

In the vertical motion, use s = ut + (1/2)at^2
with s = (20.7-2.3) m = 18.4 m, u = 0 m/s, a = g(= 10 m/s^2), t = 59/v
hence, 18.4 = (1/2).(10).(59/v)^2
v = 30.76 m/s

2. Use equation: v = u + at for the vertical motion
with u = 0 m/s, a = g(=10 m/s^2), t = 59/30.76 s = 1.918 s
hence, v = 10 x 1.918 m/s = 19.18 m/s

speed of car = square-root]30.76^2 + 19.18^2] m/s = 36.25 m/s

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