Physics
posted by Kevin .
A 90 kg halfback runs north and is tackled by a 120 kg opponent running south at 4 m/s. The collision is perfectly inelastic. Just after the tackle, both players move at a velocity of 2 m/s north. Calculate the velocity of the 90 kg player just before the tackle.
a.) 3 m/s south
b.) 4 m/s south
c.) 10 m/s north
d.) 12 m/s north

Given
mA = 90 kg
MAf = 2 m/s
mB = 120 kg
MAi = 4 m/s
MAf = 2 m/s
Use the equation:::
(MA)(VAf) + (MB) (VBf) = (MA)(VAi) + (MB)(MBi)
If you have any questions, just reply back. 
north momentums:
before
90 v  120 * 4
after
(90+120) * 2
set those equal and solve for v 
10m/s