Linear momentum handball problem

[beastysk8er]

Homework Statement

A handball of mass 0.10 kg, traveling horizontally at 30 m/s, strikes a wall and rebounds at 24 m/s. What is the change in the momentum of the ball?

Homework Equations

change in momentum = mv2 - mv1

The Attempt at a Solution

Do you take 24 as negative or positive? If you take it as neative you get -2.4-3=-5.4 if you take it as positive you get 2.4-3= -.60
both answers given in the problem are either positive 5.4 or positive 6.0. Thanks for your help

 

[Doc Al]

If you take the 30 m/s velocity as positive, then you'd better take the 24 m/s as negative since it's going in the opposite direction. For the final answer they just want the magnitude of the change in momentum, which is always positive.