Question

A uniform plank of wood has a mass of 18.7kg and a length of 2.0m. A person holds the plank using both hands. The first hand exerts a downward force, f1, at one end of the plank. The second hand exerts an upward force, f2, at a distance of 50.0cm from the same end of the plank. What is the net torque on the plank about the end where the first hand is located?

1) The net torque is zero
2) The net torque is equal to the product of the downward force and the distance between the two forces
3) The net torque is equal to the product of the upward force and the distance between the two forces
4) The net torque is equal to the sum of the products of the forces and their respective distances from the end where the first hand is located

Answer 1

Without values for forces f1 and f2, the actual net torque cannot be calculated, but if the 2.0m long plank is in equilibrium when held, the net torque at the pivot point should be zero due to the equal and opposite torques produced by the forces.

Step-by-step explanation:

To determine the net torque on the plank with respect to the end where the first hand is located, we need to consider the forces applied and their distances from the pivot point. The question describes a person holding a uniform plank of wood with a length of 2.0m, where the first hand applies a force f1 downwards at one end and the second hand applies a force f2 upwards at a distance of 50.0cm from the same end. If the system is in equilibrium, meaning the net force and the net torque are both zero, the net torque would be calculated by taking the difference between the products of each force and their respective distances from the pivot point (the end where the first hand is located). Here, since we do not have values for f1 or f2, we cannot calculate the actual net torque. However, if the plank is in equilibrium, the net torque should be zero, as the forces will produce equal and opposite torques that cancel each other out.