Posted by **rachel** on Saturday, November 8, 2008 at 9:46pm.

A 0.5 kg ball is thrown horizontally towards a wall with a speed of 10 m/s. The initial velocity is chosen to be the positive x-direction for this question. The ball horizontally rebounds back from the wall with a speed of 10 m/s in the negative x-direction. What is momentum of the ball before it hits the wall, pi? What is momentum of the ball after it hits the wall, pf? What is the change in momentum of the ball, Δp? (Give both magnitude and direction for each answer.) Is momentum conserved for the ball?

- physics conservation of momentum -
**drwls**, Saturday, November 8, 2008 at 10:55pm
p is the symbol for momentum. pi means initial momentum and pf is the final momentum.

To calculate p, multiply mass M by velocity, V. They tell you what M and V are. The SIGN of V changes from + to - after the ball bounces.

Now, with that explanation, see if you can answer the questions by yourself.

- physics conservation of momentum -
**rachel**, Sunday, November 9, 2008 at 12:02am
yeah i kno how to calculate those 2. i got 5 and -5...

so is momentum conserved?

because change in momentum would be

5 - (-5) = 10

but some ppl are telling me momentum is conserved because they are the same values.

- physics conservation of momentum -
**kat**, Sunday, November 9, 2008 at 6:08am
isn't the change in momentum: Pf-Pi?

So wouldn't that mean:

-5-5=-10?

- physics conservation of momentum -
**drwls**, Sunday, November 9, 2008 at 7:09am
The momentum of the ball is not conserved because of the force applied to it by the wall. You calculated the momentum change correctly. Ignore what "some people" say.

- physics conservation of momentum -
**r2d2**, Tuesday, December 2, 2014 at 4:15pm
what's the magnitude and direction?

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