A student plays on a see-saw with her father. The student has a weight of 300 N and is seated 2.4 m from the axis of rotation. Her father balances her when he is seated 0.8 m from the axis. The father's weight is:

A. 300 N
B. 500 N
C. 700 N
D. 800 N
E. 900 N

Question

A student plays on a see-saw with her father. The student has a weight of 300 N and is seated 2.4 m from the axis of rotation. Her father balances her when he is seated 0.8 m from the axis. The father's weight is:

A. 300 N
B. 500 N
C. 700 N
D. 800 N
E. 900 N

anonymous · Answer

This is a problem in which the torque around the see-saw's axis of rotation has to be zero. Torque is given by this equation:$$T=Fd$$where T is torque; F is the force; and d is the distance at which the force is acting.  So what you have here is a situation in which the following is true:$$T _{student}=T _{father}$$Do you see, now, how to solve the problem?

anonymous · Answer

Force * lever arm = force * lever arm

300N * 2.4 = father * 0.8

(300N * 2.4)/0.8 = 900N