A ball of mass 0.440 kg moving east (+x direction) with a speed of 3.80 m/s collides head-on with a 0.600 kg ball at rest. If the collision is perfectly elastic, what will be the speed and direction of each ball after the collision?

Answer 1

Let
u=vel. before, and
v=vel. after collision
velocities are positive in +x direction.

Momentum is conserved for elastic and non-elastic collisions:
∑mu = ∑mv

If the collision is perfectly elastic, then kinetic energies are conserved before and after collision :
∑ (1/2)mu² = ∑(1/2)mv².

Since all velocities before collision are known, there are two equations to solve for two unknowns, v1 and v2.