Question

Ball X has a mass of 8kg and is moving toward ball Y (which is sitting still) at 2m/s. After they collide, ball X is
sitting still. How fast is ball Y moving after the collision if it has a mass of 4kg?

Answer 1

Answer:

v = 4 m/s

Explanation:

Given :

Ball X :

Mass, m1 = 8kg ;

Initial Velocity, u1 = 2 m/s

Final velocity, v1 = 0

Ball Y:

Mass, m2 = 4kg ;

Initial Velocity, u2 = 0 m/s

Final velocity, v2 = v

(m1u1 + m2u2) = (m2v2 + m1v1)

(8*2 + 4*0) = (4*v + 4*0)

16 + 0 = 4v + 0

16 = 4v

v = 16 / 4

v = 4 m/s

Answer 2

Answer:

Explanation:

This is the Law of Momentum Conservation which for us looks like this:

$[m_xv_x+m_yv_y]_b=[m_xv_x+m_yv_y]_a$ and that should look familiar to you if this is what you are doing in physics. Filling in our particular info:

[(8.0 × 2.0)+ (4.0 × 0.0)] = [(8.0 × 0.0) + (4.0v)] and

16 + 0 = 0 + 4.0v and

16 = 4.0v so

v = 4.0 in the direction of ball X