A ball with a mass of $6 k g$ $6 kg$ is rolling at $7 \frac{m}{s}$ $7 m/s$ and elastically collides with a resting ball with a mass of $3 k g$ $3 kg$ . What are the post-collision velocities of the balls?

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Answer 1 · 2016-05-11T20:31:28

$v_1^'=7/3 m/s$
$v_2^'=28/3 m/s$

$6*7+3*0=6*v_1^'+3*v_2^'" conservation of momentum"$

$42=6*v_1^'+3*v_2^'" "(1)$

$v_1+v_1^'=v_2+v_2^'" conservation of the kinetic energy"$

$7+v_1^'=0+v_2^'" (2)"$

$42=6*v_1^'+3(7+v_1^')$

$42=6v_1^'+21+3v_1^'$

$42-21=9v_1^'$

$21=9v_1^'$

$v_1^'=21/9$

$v_1^'=7/3 m/s$

$"use (2)"$

$7+7/3=v_2^'$

$v_2^'=28/3 m/s$

A ball with a mass of 6 kg6kg 6 kg is rolling at 7 m/s7ms7 m/s and elastically collides with a resting ball with a mass of 3 kg3kg3 kg. What are the post-collision velocities of the balls?