Question

A 1590 kg car moving south at 13.5 m/s collides with a 2540 kg car moving north. The
cars stick together and move as a unit after
the collision at a velocity of 5.90 m/s to the
north.
Find the velocity of the 2540 kg car before
the collision.
Answer in units of m/s

Answer 1

Conservation of momentum (northis positive, south is negative velocities):
1590 kg * (-13.5 m/s) + 2540 kg * v = (1590 kg + 2540 kg) * 5.90 m/s;
From this, v = ( (1590 kg + 2540 kg) * 5.90 m/s - 1590 kg * (-13.5 m/s) ) /
(2540 kg) = 18.04 m/s

Answer: 18.04 m/s