Momentum/Conservation of Momentum

[tallbus1]

Homework Statement

A 65.0 Kg ice skater is moving to the right with a velocity of 2.50 m/s throws a .0150 kg snowball to the right with a velocity of 32.0 m/s relative to the ground
a. What is the velocity of the ice skater after throwing the snowball? Disregard the friction between the skates and the ice.
b. A second skater initially at rest wit ha mass of 60.0 kg catches the snowball. What is the velocity of the second skater after catching the snowball in a perfectly inelastic collision?

Homework Equations

Pf=Pi
P=mv

The Attempt at a Solution

Here's my issue, I don't see how to find the affect of the impulse on the velocity
a.Pf=Pi
mfvf=mivi
(65.0)(vf)=(65)(2.5)

b.
Pf=Pi
mfvf=mivi
(60kg)(?)=0 <At rest

Am I on the wrong track? Can I use F=p/t?

Thanks.

 

[roflwaffle]

use conservation of momentum, don't think about impulse. if you need more help, ask.
update: so I am procrastinating from doing my own homework, so i did your problem and scanned it

 

[tallbus1]

Right but what I don't understand is how to take into account the skater's initial velocity, final velocity, and the effect the throwing has on the velocity

 

[Dougggggg]

You have the momentum set up with just the skater. When using conservation of momentum, it has to be the whole system (anything affecting the momentum).

 

[roflwaffle]

[PLAIN]http://img827.imageshack.us/img827/1201/img023o.jpg

also check out http://www.khanacademy.org/video/introduction-to-momentum?playlist=Physics"

and http://www.khanacademy.org/video/momentum--ice-skater-throws-a-ball?playlist=Physics"

 

[Dougggggg]

Hey man, don't just give the answers away. The idea of this section is for homework help, not homework solutions.

 

[tallbus1]

Well the once sentence answers weren't really getting me anywhere. So the answer by him actually helped. I realized that I needed to be doing, and it gave me a better overall understanding of the section

 

[tallbus1]

So you can incorporate the momentum of multiple objects into a conservation of momentum problems? Then add them together to solve for one variable?

 

[Dougggggg]

Basically what I was trying to say was that momentum is based on a whole system. So the intial momentum of both the snowball and the skater, will equal the final momentum of them both.

 

[tallbus1]

So if for example, the problem went on to say the first skater then threw one more snowball, I could add a m3 and a v3?

 

[roflwaffle]

yes! (if you do it the right way :P)

 

[roflwaffle]

Hey man, don't just give the answers away. The idea of this section is for homework help, not homework solutions.

if you never see the right way to do it, how can one expect you to do it correctly? one sentence responses are not what anyone needs for any type of help.With this he can study the solution to the problem and use it as a model for similar problems and not need to come to pf for this type of problem again.

(i should have just said a picture is worth a thousand words)

 

[tallbus1]

Regardless, thank you both for the answers, today in class I had a very easy time and inelastic VS. Elastic Momentum was a breeze, also systems with 3 or 4 objects were made easier with the help of you guy's insight.

Thank you