Homework Help: Linear Momentum

1. Apr 12, 2004

3.14159265358979

1) A 2.0 kg steel ball rolling at 5.0 m/s [W] strikes a second steel ball of equal mass at rest. After a the collison, the first ball is deflected [N35W] at 3.0 m/s. Determine the velocity (and direction) of the second ball. (the answer in the back of the book is 4.1 m/s [s37w], but i got something different) thanks!

2. Apr 12, 2004

Chen

What is the total momentum of the two balls before the collision, in the [NS] axis? Zero. So what should be the total momentum of the two balls after the collision along the same axis? Zero as well. So you have one equation, for the conservation of momentum in the [NS] axis, with one unknown - the velocity of the second ball after the collision. (In case this is what you are missing, the angle between the velocities of the two balls after the collision is 90 degreesm, because the masses of the balls are equal. If you cannot use this piece of information, or need to prove it first, just write down the equation for the conversation of momentum in the second axis, [WE], and introduce another variable into your equations - the angle of the velocity of the second ball.)

Last edited: Apr 12, 2004
3. Apr 12, 2004

3.14159265358979

i still don't understand how they got that answer! help please? thank you..

4. Apr 12, 2004