Physics football tackle problem

[briguy1812]

Homework Statement

a running back with a mass of 80kg and a speed of 8m/s collides with and is held by a 120kg defensive tackle going in the opposite direction how fast must the tackle be going before the collision for their speed afterward to be zero?

Homework Equations

Linear momentum = mv
total mv before equals total mv after

The Attempt at a Solution

i was thinking that I would take mv=80x8 =640 divided by 120 =5.3m/s

 

[rock.freak667]

yes that is correct

m1v1-m2v2=0 so v2=m1v1/m2