How Does Momentum Change When a Ball Bounces Off a Wall?

[yamugushi]

1. Homework Statement
A ball is rolled into a wall and bounces back at the same speed, the change in momentum is?

2. Homework Equations
Ein = Eout

3. The Attempt at a Solution
I thought it was m(v) but I got it wrong (doing test corrections ATM)

Note I'm having trouble editing, so I made a new thread, I am not trying to spam.

 

[rock.freak667]

If the velocity before impact is v, what is the velocity after impact?

(remember, velocity is a vector quantity, so direction is important)

 

[yamugushi]

So it's be -mv... but there aren't any negative answers:
I have
0
1.5
.5
2
and what I answered MV (all above are times MV as well)

 

[rock.freak667]

So it's be -mv... but there aren't any negative answers:

So momentum before is mv, and momentum after is -mv, so that change in momentum is ?

 

[yamugushi]

2mv?

 

[rock.freak667]

2mv?

is that one of the answers?

 

[yamugushi]

is that one of the answers?

yes, the answers were:
0mv
1mv
1.5mv
.5mv
2mv

 

[Winzer]

Just to note:

The original velocity must have been negative. The initial momentum was $$P_1=-mv$$.
Following the bounce, the final momentum is $$P_2=mv$$.
Hence the positive answer: P2-P1=2mv
Either way the magnitudes are the same.

 

[rock.freak667]

Just to note:

The original velocity must have been negative. The initial momentum was $$P_1=-mv$$.
Following the bounce, the final momentum is $$P_2=mv$$.
Hence the positive answer: P2-P1=2mv
Either way the magnitudes are the same.

Yes the magnitudes are the same, but it didn't have to be negative. It depends on the direction you choose as positive.