You are asked to find the boy’s lever arm.
You are given the two masses and the cat’s lever arm.
Use: = r F, and F = mg
Solve for the cat: = (2 m)(4 kg)(9.8 N/kg) = +78.4 N⋅m
Solve for the boy: = (d )(50 kg)(9.8 N/kg) = -490 d
For rotational equilibrium, the net torque must be zero.
0= 78.4 – 490d d = 0.16 m. The boy must sit 16 cm from center.
Solve a rotational equilibrium problem
A boy and his cat sit on a seesaw. The cat has a mass of 4 kg and sits 2 m from the center of rotation. If the boy has a mass of 50 kg, where should he sit so that the see-saw will balance?