1. A 5-kg steel ball traveling horizontally strikes a massive wall at 10m/s and
ID: 1350692 • Letter: 1
Question
1. A 5-kg steel ball traveling horizontally strikes a massive wall at 10m/s and rebounds elastically, returning horizontally back on its original path at 8 m/s. If it is in contact with the wall for 0.20 seconds what is the average force exerted by the wall on the ball?
2. A railroad car (m = 2 x 104 kg) moving at 2.80 m/s collides and couples with two coupled railroad cars each of the same mass as the single car and moving in the same direction at 1.20 m/s. What is the speed of the three coupled cars after the collision?
Explanation / Answer
1) Apply Impulse = change in momentum
F_avg*t = m*(v2 - v1)
F_avg = m*(v2 - v1)/
= 5*(8 -(-10))/0.2
= 450 N
2) let m1 = m
m2 = 2*m
v1 = 2.8 m/s
v2 = 1.2 m/s
after the colsion, V = ?
Apply conservation of momentum
m1*v1 + m2*v2 = (m1+m2)*V
V = (m1*v1 + m2*v2)/(m1+m2)
= (m*2.8 + 2m*1.2)/(m + 2*m)
= 1.73 m/s