1.) You are investigating an accident in which two cars of similar makes collide
ID: 1378226 • Letter: 1
Question
1.) You are investigating an accident in which two cars of similar makes collided partway up a hill. The hill road is inclined at 20 degrees above the horizontal and the mangled wreckages of the two cars were found about 35 meters uphill. An eyewitness states that the car coming down the hill had managed to brake and come to a stop just before the collision, but the car going up the hill continued to cruise at a constant speed hitting the other car head-on. She also says that after the collision, the two cars---now effectively stuck together---slid about 15 meters before coming to rest. You want to determine the speed of the car going uphill before the collision. You make some preliminary measurements of the coefficient of friction between sliding rubber and the road surface and find that it is about 0.65.
Explanation / Answer
F(friction) = umgsin20 = 1.84*m
F(gravity) = mgcos20 = 9.208*m
F(net) = ma
(1.84+9.208)*m = ma
a = -11.05m/s^2 (slowing down)
2ad = v^2 - v0^2
2(-11.05)(10) = 0 - v0^2
v0^2 = 221
v0 = 14.9m/s
m1v2 + m2v2 = 2mv
v1 = 2v
v1 = 2*14.9 = 29.7m/s
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