Question

Now consider the collision represented in the animation below. Let's assume that the two balls are sliding on a frictionless, horizontal surface. Do not assume that this collision is elastic (though it might be).

Here's what's given:

The direction of +x is to the right.

The blue ball has twice the mass of the red. Let's make them mb = 2 kg and mr = 1 kg.

The red ball is initially stationary.

The initial velocity of the blue ball, vbi, is 6 m/s, and its final velocity, vbf, is 2 m/s.

Find the final velocity, vrf, of the red ball, in meters per second. Enter only a single number (without units) before submitting. If your answer isn't an integer, you've made a mistake somewhere !

Answer 1

Mass of blue ball = m_b = 2 kg

Mass of red ball = m_r = 1 kg

Initial velocity of blue ball = V_bi = 6 m/s

Final velocity of blue ball = V_bf = 2 m/s

Initial velocity of red ball = V_ri = 0 m/s

Final velocity of red ball = V_rf

By conservation of linear momentum,

m_bV_bi + m_rV_ri = m_bV_bf + m_rV_rf

(2)(6) + (1)(0) = (2)(2) + (1)V_rf

V_rf = 8 m/s

Final velocity of the red ball = V_rf = 8 m/s