A 2590-kg van runs into the back of a 821-kg compact car at rest. They move off

Question

A 2590-kg van runs into the back of a 821-kg compact car at rest. They move off together at 8.5 m/s. Assuming the friction with the road is negligible, calculate the initial speed of the van.
m/s

The velocity of a 621-kg auto is changed from 10.0 m/s to 44.0 m/s in 70.2 s by an external, constant force.
(a) What is the resulting change in momentum of the car?
kg · m/s

(b) What is the magnitude of the force?
N


A 92-kg fullback, running at 5.0 m/s, attempts to dive directly across the goal line for a touchdown. Just as he reaches the line, he is met head-on in midair by two 73-kg linebackers both moving in the direction opposite the fullback. One is moving at 2.0 m/s, the other at 4.0 m/s. They all become entangled as one mass.
(b) What is the velocity of the football players after the collision? (Take the positive direction to be the initial direction of the fullback.)

Explanation / Answer

Conserving momentum 2590u + 0 = (2590 + 821)(8.5) implies u = 11.19 m/s Impulse = Fx t = change in momentum F x 70.2 = 621 ( 44 - 10) implies F = 300.77 N Conserve momentum of the three players 73(2) + 73(4) - 92(5) = (73+73+92)v implies v = -0.092 m/s So the three of them move at 0.092m/s in the same direction as the initial direction of the fullback.

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