Problem 9-10

Notes:

1. There is an upward force at the pivot. This upward force should equal to the sum of the child and adult weights (30g+70g = 980N) so that the equilibrium condition "Total force = 0" is satisfied.
2. The pivotal point is chosen as the origin so that the calculation can be done without knowing the upward force at the pivot. This force is not required by the problem.