You stand in the middle of a road 1 and throw a rubber bouncy ball at a truck 2

Question

You stand in the middle of a road1 and throw a rubber bouncy ball at a truck2 that is coming straight towards you at 75 miles per hour. You throw the ball at 95 miles per hour. The ball hits the truck and elastically bounces back towards you. How fast is it moving after bouncing off the moving truck?


1You should not really do this.
2Nor this.

Two carts are sitting on a frictionless track. Cart 2 (mass 4M) is stationary, but Cart 1 (mass 3M) is coming at it at a speed of 4V. They collide and, thanks to the magic of Velcro, stick together. What is their speed after the collision?
V

Explanation / Answer

For elastic collision,

velocity of approach = velocity of seperation.

{ after collision, there will be neglible change in velocity of truck,

hence for truck, vf = vi = 75 mph }

(75 + 95) = v - 75

v = 245 mph

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