Posted by Lui on .
A 1400 kg car moving south at 11.5 m/s collides with a 2800 kg car moving north. The cars stick together and move as a unit after the collision at a velocity of 5.24 m/s to the north. Find the velocity of the 2800 kg car before the collision.

Momentum 
Elena,
m1 •v1  m2•v2 =  (m1+m2) •u,
v2 ={ m1 •v1 + (m1+m2) •u}/m2 =
={(1400•11.5) + 1400+2800) •5.24}/2800 = =13.61 m/s