Question

In an elastic collision:

mass a is 1kg, and is moving at 100ms^1 in the +ve x direction when it hits mass b, 10kgs at rest. Given: mass a moves off at 80 ms^1 in the -ve x direction. What's the final velocity of mass b.

Using cons of momentum, i say 2 ms^1 in the +ve x directon. Is that correct.

Thanks.

Answer 1

You are close.

1.8 m/s must be the final velocity of mass b because of momentum considerations, whether energy is conserved or not.
1*100 = 1*(-80) + 10*Vb
Vb = 180/10 = 1.8

Initial kinetic enery = (1/2)*1*10^4 = 5000 J

Final kinetic energy = (1/2)*1(80)^2 + (1/2)(10)(1.8)^2 = 3200 + 16.2 = 3216 J

The collision is NOT elastic.

You may have mistyped the first sentence