# Kinematics moving ball problem

1. Sep 24, 2015

### Speeder63

1. The problem statement, all variables and given/known data
A ball moving westward at 36 m/s hits a wall and rebounds at 27 m/s, eastward. (a) What is the change Δv in the vector velocity? (This is effectively the velocity of the rebounding ball relative to an image of it passing through the wall unaffected. It’s not the same as the 9 m/s reduction in the scalar speed!)

(b) Find the acceleration during the impact if that lasts 0.14 s.

2. The attempt at a solution

For change in velocity I had 9 m/s eastward. I don't know if that is correct.

2. Sep 24, 2015

### andrewkirk

If we take positive direction as being Eastward then the ball's velocity prior to impact is -36 m/s (that's a minus sign there).

What is the velocity after impact?

What is the second one minus the first one?

3. Sep 24, 2015

### Speeder63

so the velocity after impact is -9m/s.
would I use this to find the acceleration?

4. Sep 24, 2015

### Speeder63

would I use that to find the acceleration?

5. Sep 24, 2015

### andrewkirk

No.
The absolute value of the velocity has to equal the speed.

6. Sep 24, 2015

### Speeder63

So if the velocity is -9m/s the absolute velocity is 9m/s?