Solve for mass using a graph of a collision

[B3NR4Y]

Homework Statement

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.

Homework Equations

$m_{s} \Delta v_{s} = -m_{A} \Delta v_{A}$

The Attempt at a Solution

I calculated Δv_A 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 Δv_s 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) = - m_A (kg) * (-2 m/s). Which when I multiplied out, and solved for m_A. I got 2.13 kg. Which, apparently, is wrong. Please help!

 

[Greg Bernhardt]

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