Need help with a seesaw torque question.

[paperdoll]

Homework Statement

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.

Homework Equations

torque= F * r (perpendicular distance?)
F=ma

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.

 

[Doc Al]

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.

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

 

[paperdoll]

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

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

 

[Doc Al]

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

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