Mom and Collision?

Question

A 90 kg fullback runs east with 4.9 m/s. He is tackled by 94 kg opponent running north with 3 m/s. The collision is perfectly inelastic.
Find the speed and dircetion of the players after tackle.

After an elastic collision, how do you find the energy lost(like mechanical energy)?

Answer 1

The post collision velocity vf = (m1v1+m2v2)/(m1+m2).
The v's are vectors, so the addition of m1v1+m2v2 must keep the x and y components separate. This is important in this problem since the collision is not head-on.
I think you mean "after an inelastic collision", right? The lost energy after an inelastic collision is the difference between final KE which = (m1+m2)vf^2/2, and the total initial KE which = m1v1^2/2 + m2v2^2/2. In this calculation, you use the magnitudes of vf, v1 and v2 since energy is not a vector.