Question

Two bumper cars run into each other at the fair. Jack and his car have a mass of 200 kg and Jill and her car have a mass of 190 kg. Jack runs into Jill going 4 m/s to the right. Jill bounces off to the right at a speed of 4.2 m/s and Jack bounces off at a speed of 2 m/s to the left. What was Jill’s initial velocity?

Answer 1

In a collision the linear momentum is conserved, this means that:

$p_i=p_f$

where:

$p=mv$

Applying the conservation of momentum we have that:

$\begin{gathered} 200(4)+190v=200(-2)+190(4.2) \\ 190v+800=398 \\ 190v=398-800 \\ 190v=-402 \\ v=-\frac{402}{190} \\ v=-2.12 \end{gathered}$

Therefore Jill's initial velocity has a magnitude of 2.12 m/s and points left.