The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque?
A) A
B) B
C) C
D) D
E) E

Question

The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque? 
A) A 
B) B 
C) C 
D) D 
E) E

Quizplus · Accepted Answer

To use a single equation to find the force exerted on the rod by the rope, we need to consider both the torque due to the force of the rope and the torque due to the friction between the rod and the wall. These torques will balance each other out when the rod is in equilibrium.

The torque due to the force of the rope acts at point E, perpendicular to the rod and equal to the force of the rope times the perpendicular distance from point E to the line of action of the force.

The torque due to the friction acts at point C, perpendicular to the rod and equal to the friction force times the perpendicular distance from point C to the line of action of the force.

Therefore, we should place the reference point for computing torque at point C, so that we can easily take into account both torques and solve for the force of the rope.

The Diagram Shows a Stationary 5-Kg Uniform Rod (AC), 1