Four happy kids are lining up and jumping off a diving board one after another. The kids, each with a mass of 40 kg, are situated as in the above figure, and the uniform board has a total mass of 60 kg. Calculate the force on the support closest to the water.
A) 3140 N, up
B) 4320 N, down
C) 4320 N, up
D) 3140 N, down
E) 3920 N, down

Question

Four happy kids are lining up and jumping off a diving board one after another. The kids, each with a mass of 40 kg, are situated as in the above figure, and the uniform board has a total mass of 60 kg. Calculate the force on the support closest to the water.
A) 3140 N, up 
B) 4320 N, down 
C) 4320 N, up 
D) 3140 N, down 
E) 3920 N, down

Quizplus · Accepted Answer

First, we need to find the total weight of the system. Each child has a mass of 40 kg, so the weight of four children is:

W_children = 4(40 kg) x 9.8 m/s^2 = 1568 N

The diving board has a mass of 60 kg, so its weight is:

W_board = 60 kg x 9.8 m/s^2 = 588 N

The total weight of the system is:

W_total = W_children + W_board = 2156 N

Since the system is in equilibrium, the upward force on the support closest to the water must be equal in magnitude and opposite in direction to the total weight of the system. Therefore, the force on the support closest to the water is:

F_support = W_total = 2156 N

Since the force is equal in magnitude and opposite in direction to the weight, the answer is (C) 4320 N, up.

Four Happy Kids Are Lining Up and Jumping Off a Diving