# Physics 11 help please ?

1. Dec 15, 2008

### roxxyroxx

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

A 55 kg student wearing skates stands at rest on a frictionless horizontal ice surface. She throws a 10 kg backpack horizontally with a speed8.3 m/s .
What is the velocity of the student after she throws the backpack?

2. Relevant equations

F$$\Delta$$t = m$$\Delta$$v

3. The attempt at a solution
so the answer should be 1.5 m/s [N] and i got this by dividing 10 kg (backpack) by 55 kg (student) and then multiplying that answer by 8.3 m/s . is this the right way or is there a proper formula i should follow?
thanks !

2. Dec 15, 2008

### Staff: Mentor

That's correct. The impulse given to the backpack will be exactly equal and opposite to the impulse given to the student. Thus:
mstudent*vstudent = mbackpack*vbackpack

Just solve for vstudent.

3. Dec 15, 2008

### roxxyroxx

great, thanks !