Calculating the change of momentum in a system

[cheetogrease]

Homework Statement

A ball with momentum of 10 kg-m/s [E] hits an object and rebounds with momentum of 6 kg-m/s [W]. What was the change in momentum?

Homework Equations

delta p=p(final)-p(initial)

The Attempt at a Solution

delta p=p(final)-p(initial)
delta p=(6 kg-m/s)-(10 kg-m/s)
delta p= -4 kg-m/s

This problem seems so simple, and yet it's in the middle of a worksheet full of really hard problems, so I just wanted to make sure I'm doing it right.

 

[grzz]

I am assuming that impact is head on i.e. there are no angles involved.

Do not forget that momentum is a VECTOR.
Hence if to the RHS one takes it as positive, it must be taken as negative when it reverses direction.