Questions: I am sitting on a seesaw opposite my young nephew. The seesaw is 12.2 feet long and has a pivot in the middle. I weigh 120.1 lbs while my nephew weighs 31.6 lbs . What is the magnitude of the initial net torque on the seesaw (in ft -lbs)?

Solution Steps

We need to calculate the net torque on a seesaw. The seesaw is 12.2 feet long with a pivot in the middle, meaning each side is 6.1 feet long. The weights of the individuals are given, and we need to find the torque produced by each person and then determine the net torque.

Torque (\(\tau\)) is calculated using the formula: \[ \tau = r \times F \] where \(r\) is the distance from the pivot and \(F\) is the force (weight).

For the person weighing 120.1 lbs: \[ \tau_1 = 6.1 \, \text{ft} \times 120.1 \, \text{lbs} = 732.61 \, \text{ft-lbs} \]

For the nephew weighing 31.6 lbs: \[ \tau_2 = 6.1 \, \text{ft} \times 31.6 \, \text{lbs} = 192.76 \, \text{ft-lbs} \]

Assuming the person weighing 120.1 lbs is on the left side and the nephew is on the right side, the torque due to the person will be counterclockwise (positive) and the torque due to the nephew will be clockwise (negative).

The net torque is the sum of the individual torques, taking into account their directions: \[ \tau_{\text{net}} = \tau_1 - \tau_2 = 732.61 \, \text{ft-lbs} - 192.76 \, \text{ft-lbs} = 539.85 \, \text{ft-lbs} \]

Final Answer