Question

A 2.5 kg ball moving at 4.2m/s collided with a 2.5 kg stationary ball. If the first ball is at rest after the collision what is the velocity of the second ball

Answer 1

We need to apply the conservation of momentum formula

$m1u1+m2u2=m1v1+m2v2$

Where m1 and m2 are the masses, u1 and u2 are the initial velocities of each mass, and v1 and v2 are the final velocities of each mass

we have

m1= 2.5 kg

u1= 4.2 m/s

m2=2.5 kg

u2= 0 m/s

v1=0 m/s

v2=?

we substitute

$2.5(4.2)+2.5(0)=2.5(0_{})+2.5(v_2)$

therefore

$v2=4.2\text{ m/s}$

ANSWER

v2=4.2 m/s