What Is the Change in Velocity and Acceleration of a Rebounding Ball?

[Speeder63]

Homework Statement

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.

 

[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?

 

[Speeder63]

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

 

[Speeder63]

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?

would I use that to find the acceleration?

 

[andrewkirk]

so the velocity after impact is -9m/s.

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

 

[Speeder63]

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

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