Ricocheting Bullet (elastic collisions)

1. Oct 20, 2008

needphyshelp

1. The problem statement, all variables and given/known data
.100-kg stone rets on a frictionless, horizontal surface. A bullet of mass 6.00g, traveling horizontally at 350 m/s, strikes the stone and rebounds horizontally at right angles to its original direction with a speed of 250 m/s. (a) Compute the magnitude and direction of the velocity of the stone after it is struck.

2. Relevant equations
Kfinal=Kinitial
Pfinal=Pinitial

3. The attempt at a solution
My problem with this question is that I cannot visualize it so I do not know how to try and solve it. I am confused because the bullet is initially traveling horizontally, but then is rebounding horizontally but at a right angle to the horizontal...? I thought it was just giving me the x-component of velocity for the bullet, but wouldn't the situation described be vertical?

2. Oct 20, 2008

mgb_phys

It bounces off horizontally,
Picture it coming in from the north, hitting a 45degree angle face of the stone and bouncing off going east.

The important point is that the total momentum in each direction (eg North-South and East-West) must be the same before and after.

3. Oct 20, 2008

needphyshelp

If it is coming from the north, wouldn't it be coming in with a vertical velocity? Or is this just a matter of defining axes?

4. Oct 20, 2008

mgb_phys

North as on a map.
Or if you prefer imagine a flat piece of graph paper where the bullet is coming down the y-axis and bounces off up the x-axis.

Last edited: Oct 20, 2008
5. Oct 20, 2008

needphyshelp

ohhhhhh. that makes sense.