# Solve for mass using a graph of a collision

1. Sep 7, 2014

### B3NR4Y

1. The problem statement, all variables and given/known data
A 1-kg standard cart collides with a cart A of unknown inertia. Both carts appear to be rolling with significant wheel friction because their velocities change with time as shown in. What is the mass of cart A?

The graph below should be used to solve for the mass.

2. Relevant equations
$m_{s} \Delta v_{s} = -m_{A} \Delta v_{A}$

3. The attempt at a solution

I calculated ΔvA using the graph, to be ~-2 m/s, because the velocity before the collision is ~4 m/s and afterwards it is ~2 m/s, so 2(m/s) - 4(m/s) = -2 m/s, simple. I calculated Δvs to be ~4.25 m/s because the velocity changes from 0 m/s to 4.25 m/s. So the equation becomes 1 (kg) * 4.25 (m/s) = - mA (kg) * (-2 m/s). Which when I multiplied out, and solved for mA. I got 2.13 kg. Which, apparently, is wrong. Please help!

2. Sep 8, 2014