Question

HELP!!
Object A with a mass of 1.5 kilograms is moving with a velocity of +11.2 meters/second (moving in the +x direction). It has a perfectly elastic collision with stationary object B that has a mass of 4.5 kilograms. After the collision, object B travels with a velocity of +5.6 meters/second. What is the final velocity for object A?
I'll give out METALS to the right answer!!!

Answer 1

This is a "momentum" question. That is, energy is conserved after impact. The idea here is that the total momentum in the objects is the same before and after. The equation you set up is:
M1V1 + M2V2 = M1(V1)' + M2(V2)'
Givens:
M1 = 1.5kg
M2 = 4.5kg
V1 = 11.2 m/s
V2 = 0 m/s
(V2)' (after impact) = 5.6 m/s

Subbing into the equation above, we get:
(1.5)(11.2) + (4.5)(0) = (1.5)(x) + (4.5)(5.6)
Rearrange and calculate: x = -5.6

What this means is, object 1 is moving 5.6 m/s in the opposite direction now. Since we have 100% elastic conditions, there is no energy absorbed by the objects.

There is your answer.