Question

A ladder, length L, with mass M, leans against a frictionless wall at an angle of θ=70° as shown.

1) If the ladder is in static equilibrium,
The net force is zero but the net torque is not.
The net torque is zero but the net force is not.
The net force and net torque are both zero.
Neither net force nor net torque is zero.
2) Which of these free body diagrams best represents the forces on the ladder?
3) At which of the following locations can we put the rotation axis we use when calculating torques?
Only at the center of the ladder.
Only at the bottom left end of the ladder.
Only at the top right end of the ladder.
We can choose any of these locations for the rotation axis.
4) For the rest of these problems, we're using the top right end of the ladder as our pivot point. What is the magnitude of the torque from the force of gravity, around this point?
L* M g* sin (θ)
L* M g* cos (θ)
(L/ 2)* Mg g* sin (θ)
(L/ 2)* M g* cos (θ)

Answer 1

1 - The net force and net torque are both zero.
2 -The third free body diagram represents the forces on the ladder.
3 -We can choose any of these locations for the rotation axis.
4- (L/2)Mgsin(θ) is the magnitude of the torque from the force of gravity, around the top right end of the ladder.