change in momentum?

Question

A 4.0 kg ball is traveling at 10 m/s and strikes a wall. The 4.0 kg ball bounces off the wall wih a velocuty of -9.8 m/s. The change in momentum of the ball is??

a) -79.2
b) 130
c) -260
d) 24
e) -56

please help/explain thanks

Answer 1

The change in velocity is 19.8 m/s in the negative direction, because -9.8 - 10 = -19.8. The change in momentum is equal to the product of mass and the change in velocity, or (4 kg)(-19.8 m/s) = -79.2 kg-m/s, answer a).

Answer 2

The answer is -79.2 kgm/s (kilogram meters/sec.) How I got this answer and you can check my source if you'd like it might explain it better, in fact it probably will.
As long as you are working with only one dimension meaning that your ball (or other object) moves in only one direction whether forwards or backwards momentum is simply mass times volume. (p=mv) In order to get the change in momentum you just figure out the initial and the final momentum and subtract the initial from the final. So in your example your ball had 4kg x 10 m/s = 40 kgm/s going to the right (that is your initial momentum) and after it hit the wall it had 4kg x -9.8 m/s (the negative here means that it switched its direction exactly) which equals -39.2 kgm/s. In order to get the change the momentum you subtract the initial from the final. -39.2 kgm/s - 40 kgm/s = -79.2 kgm/s.

Answer 3

Initial momentum = m x v = 4.0 x 10 = 40 kg.m/s
Final momentum = m x v = 4.0 x (-9.8) = - 39.2 kg.m/s
(negative because velocity is in the opposite direction to initially)
Change in Momentum = final - initial
= -39.2 - 40 = -79.2 (if inwards to the wall is the positive direction)

Answer 4

initial momentum = 4*10 = 40
final momentum = -9.8*4= -39.2

Change in momentum = (-39.2) - (40) = -79.2

answer (a)