Velocity Calculation - ball bouncing off a wall at an angle

[Molly1235]

Velocity Calculation -- ball bouncing off a wall at an angle

Question:

"A ball is locked at 45 degrees towards a wall at 4 m/s. It bounces away from the wall at an angle of 45 degrees at 3 m/s. Find the change in velocity of the ball at the bounce."

My attempt:

So I know that change in velocity = v-u.

Therefore I thought that the answer would be 3 - -4 (3+4) = 7 m/s at an angle of 90 degrees, however my book says the answer is 5 m/s.

I'm a little confused and would be grateful for some clarification. I'm thinking it must have something to do with it being the velocity at the bounce but I'm not sure?

Thanks in advance!
Molly

 

[Crake]

Draw the diagram.

EDIT:

I'm telling you to draw the diagram, because it'll probably help you. Try doing it with vectors.

 

[Crake]

What programs do you guys use to draw vectors and diagrams and etc? Seriously

 

[Molly1235]

I think I just manged to work it out - taken a picture but then realized I can't upload it from my mobile. I was being daft and drawing it wrong as I forgot an angle of 90 degrees forms against the wall (as in your diagram). Thank you! :)

 

[Crake]

I think I just manged to work it out - taken a picture but then realized I can't upload it from my mobile. I was being daft and drawing it wrong as I forgot an angle of 90 degrees forms against the wall (as in your diagram). Thank you! :)

You're welcome. Let me know if you need any help.

 

[Molly1235]

You're welcome. Let me know if you need any help.

Thanks - I appreciate it. I'm completely new to the world of vectors so get a little confused sometimes :')