Answer:
14.4 lb
Step-by-step explanation:
In a see-saw in equilibrium, the torque generated by one side needs to be the same generated in the other side. The torque is calculated by the product between the mass and the distance to the center of the see-saw.
The torque generated by the child is:
T1 = 60 * 3 = 180 lb*feet
So, the torque generated by the weight needs to be higher than T1 in order to lift the child.
The lowest mass is calculated when the mass is in the maximum distance, that is, 12.5 feet from the center.
So, we have that:
T2 = 180 = mass * 12.5
mass = 180/12.5 = 14.4 lb
So the lowest weight is 14.4 lb
