How Is the Change in Linear Momentum Calculated in a Collision?

[ViewtifulBeau]

A 0.118 kg mass is moving horizontally with a speed of 8.49 m/s when it strikes a vertical wall. The mass rebounds with a speed of 1.07 m/s. What is the magnitude of the change in linear momentum of the mass?

isn't the change just the difference in momentum? I did .118(8.49 - 1.07) to get .87556 kg m/s. this is wrong so i think the answer is .118(8.49+1.07) because it would be minus a negative velocity. so i got 1.128 kg m/s. but i don't know if this number should be negative or not.

 

[Fermat]

The change is, as you say, just the differnce in momentum.

But momentum is mv. And v (the velocity) is a vector and has a direction.
So deltaP = mv1 - mv2, but v1 and v2 are in opposite directions, so you have to (numerically) add them.

Since you are asked for a differnce, then take the absolute value, i.e. positive.