1) A 1055-kg van, stopped at a traffic light, is hit directly in the rear by a 6

Question

1) A 1055-kg van, stopped at a traffic light, is hit directly in the rear by a 675-kg car traveling with a velocity of +2.15 m/s. Assume that the transmission of the van is in neutral, the brakes are not being applied, and the collision is elastic. What is the final velocity of each vehicle?

2) An automobile has a mass of 2150 kg and a velocity of +18 m/s. It makes a rear-end collision with a stationary car whose mass is 2000 kg. The cars lock bumpers and skid off together with the wheels locked.

(a) What is the velocity of the two cars just after the collision?

(b) Find the impulse (magnitude and direction) that acts on the skidding cars from just after the collision until they come to a halt. (Indicate direction by the sign of the impulse.)

(c) If the coefficient of kinetic friction between the wheels of the cars and the pavement is ?k = 0.70,

determine how far the cars skid before coming to rest.

Explanation / Answer

Remember that KE is conserved for elastic collisions. That equation is just saying that the KE of the car before the collision is equal to the KE of the car and of the van after the collision.

From conservation of momentum:

m1vo1 + m2vo2 = m1vf1 + m2vf2 --- (1)

you also have:

1/2m1vf1^2 + 1/2m2vf2^2 = 1/2m1vo1^2 + 0 ---- (2)

Now you have two equations and two unknowns. You can solve for both of them.

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