Two weights are hanging on a 60-cm long,100-g mass uniform wooden bar as shown in the figure.Is this system in equilibrium?
A)Yes
B)No
C)It cannot be determined.
D)It depends on value of normal force.

Question

Two weights are hanging on a 60-cm long,100-g mass uniform wooden bar as shown in the figure.Is this system in equilibrium? 
A)Yes 
B)No 
C)It cannot be determined. 
D)It depends on value of normal force.

Quizplus · Accepted Answer

For the system to be in equilibrium, the sum of all forces acting on the system must be zero, and the sum of all torques (or moments) acting on the system about any point must also be zero.

In this case, the gravitational forces acting on the weights cause a torque that tends to rotate the bar in a clockwise direction, while the normal force acting at the point of support (where the bar is hanging from the hook) causes a torque that tends to rotate the bar in a counterclockwise direction.

Since the bar remains stationary, we know that the net force acting on the system is zero. Moreover, the torques produced by the weights and the normal force cancel each other out, since they act in opposite directions and are equal in magnitude (due to the symmetry of the bar and the weights). Therefore, the system is in equilibrium, and the answer is A) Yes.

Two Weights Are Hanging on a 60-Cm Long,100-G Mass Uniform