<1> An automobile of mass 1500kg moving at 25m/s collides with a truck of mass 4

Question

<1>

An automobile of mass 1500kg moving at 25m/s collides with a truck of mass 4500kg at rest. This time, the car and the truck bounce off each other completely elastically. What is the final velocity of the truck after the collision? Call the direction of the automobile before the collision positive.

<2>

An automobile of mass 1500kg moving at 25m/s collides with a truck of mass 4500kg at rest. This time, the car and the truck bounce off each other completely elastically. What is the final velocity of the car after the collision? Call the initial direction of the automobile positive.

Explanation / Answer

For completely inelastic collision,

m1v1i + m2v2i = (m1 + m2)v

as they have the same velocity after the collision.

Solving for v,

v = 6.25 m/s   [ANSWER, PART A]

***********************

For elastic collisions, momentum and energy are conserved,

m1v1i + m2v2i = m1v1f + m2v2f

1/2m1v1i^2 + 1/2 m2v2i^2 = 1/2m1v1f^2 + 1/2m2v2f^2

Thus, solving for the new velocities,

v_car = -12.5 m/s   [opposite its initial direction]

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