# Homework Help: Ice skator throwing gloves to mvoe

1. Oct 21, 2011

### JayHakimi1

1. The problem statement, all variables and given/known data

An amateur skater of mass M is trapped in the middle of an ice rink and is unable to return to the side where there is no ice. Every motion she makes causes her to slip on the ice and remain in the same spot. She decides to try to return to safety by throwing her gloves of mass m in the direction opposite the safe side.

If she does move, calculate her velocity v-girl relative to the Earth after she throws the gloves, otherwise enter 0. (Use the following as necessary: m, M, and v-gloves).

2. Relevant equations

change in momentum = final momentum - initial momentum

3. The attempt at a solution

using the equation above i got that

v→ girl = (m/M) v→gloves

(i tried to show that its a vector above.)

but the answer is wrong, any suggestions?

2. Oct 21, 2011

### grzz

What is the initial momentum?

3. Oct 21, 2011

### JayHakimi1

Re: Ice skator throwing gloves to move

its not given, you have to solve the velocity using variable. No number involved

4. Oct 21, 2011

### grzz

Let us assume that the skater is initially at rest.
Then what is the initial momentum?

5. Oct 21, 2011

### JayHakimi1

it would be zero

6. Oct 21, 2011

### grzz

Correct.
Then what is the final momentum?

7. Oct 21, 2011

### JayHakimi1

either 0 or M v girl

8. Oct 21, 2011

### grzz

If the initial momentum was 0, what does the Principle of Conservation of Momentum tell us?

9. Oct 21, 2011

### JayHakimi1

That the final momentum has to equal to zero?

10. Oct 21, 2011

### grzz

Correct!
So the momentum of the girl must be equal in magnitude and opposite in direction to that of the glove.

11. Oct 22, 2011

### JayHakimi1

so it like thi

v girl = -(m glove* v glove)/m girl

right?

12. Oct 23, 2011

### grzz

right.

13. Oct 23, 2011

### JayHakimi1

but the website says that answer is wrong. IDK why tho

14. Oct 23, 2011

### grzz

The Physics I know tells me that if the total initial momemtum of system in a certain direction is zero then the final total momentum in that direction is zero also so long as there are no resultant forces on the system in that given direction.

So the momentum of the girl must be equal in magnitude and opposite in direction to that of the glove.