Question

A 1000 kg car travels at 20 m/s and rear ends an 800 kg car at rest. If they stick together, what is their final velocity after colliding?

A 2 kg block with initial velocity 2 m/s collides with a 4 kg block at rest and rebounds with velocity -0.5 m/s. Was the collision elastic? If not, how much energy was lost?

Answer 1

Here ,

let the final velocity after colliding is v

Using conservation of momentum

1000 * 20 + 800 * 0 = (1000 + 800) * v

v = 11.11 m/s

the final velocity after colliding is 11.1 m/s

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let the velocity of 4 Kg is v

Using conservation of momentum

2 * 2 + 4 * 0 = 2 * (-0.50) + 4 * v

v = 1.25 m/s

No, this is not elastic collision

energy lost = 0.50 * 2 * 2^2 - (0.50 *2 * 0.50^2 + 0.50 * 4 * 1.25^2)

energy lost = 0.63 J

the energy lost is 0.63 J