# Need help with a seesaw torque question.

1. Jan 11, 2012

### paperdoll

1. The problem statement, all variables and given/known data
Halle and Susan, each of mass 40 kg are sitting at opposite ends of a playground seesaw. The seesaw is stationary in the horizontal position and is 4.50 m long. Susan decides to jump off. Calculate the size of the unbalanced torque that now acts on the seesaw.

2. Relevant equations
torque= F * r (perpendicular distance?)
F=ma

3. The attempt at a solution
I'm not sure how to find the perpendicular distance from the line of action of the force to the axis of rotation. I think F would be 40*9.8=392 N but I don't know how to find the "r" value.

2. Jan 11, 2012

### Staff: Mentor

How far is she from the pivot of the seesaw? (You're given the full length of the seesaw.)

3. Jan 11, 2012

### paperdoll

It doesn't state the value in the question so I guess you are supposed to assume that she is half way. So 4.5/2=2.25 m

4. Jan 11, 2012

### Staff: Mentor

Yes, that's what I would assume. The axis of the seesaw is in the middle and she is sitting at one end.