Torque AP Physics

A rod on a horizontal tabletop is pivoted at one end and is free to rotate without friction about a vertical axis, as shown in the diagram.  A force F is applied at an angle θ to the rod.  If F were to be applied perpendicular to the rod, at what distance from the axis should it be applied in order to produce the same amount of torque?

• L sin θ

• L cos θ

• L 

• L tan θ

Rank the magnitude of the torque the signs exert about the point at which the rod is attached to the side of the building. From Greatest to Least.

• B

• D

• C

• A

Answer explanation

Answer: B > D > C > A.

The torque depends on the weight of the sign (mg) times the distance from the line of action of this weight to the

point of attachment. The line of action of the weight is along the rope that is suspending the sign, which is one

rod length (L) away from the attachment point in cases B and D, closer than that in case C, and closer yet (0.5L)

in case A. Since A and C have the smallest masses and C has the smallest distance, A will be larger than C, which

will be the smallest. Since B and D have the largest masses and the largest distances, they will have the largest

torques, with B > D.

If a system is in static equilibrium, it must have the following 2 conditions:

• ∑τ=0

• Constant acceleration

• ∑F=0

• Positive forces only

What is the definition of torque in physics?

• The rate of change of velocity

• The force applied perpendicular to the lever arm

• The energy stored in a system

• The mass of an object

Which of the following equations represents torque?

If a force of 10 N is applied at a distance of 2 meters from the pivot, what is the torque?

• 5 Nm

• 10 Nm

• 20 Nm

• 30 Nm

In which direction does torque act?

• Parallel to the force

• Perpendicular to the lever arm

• Along the lever arm

• Opposite to the force

What is the unit of torque?

• Newton

• Joule

• Newton-meter

• Watt

A wrench is used to apply a force of 15 N at a distance of 0.5 meters from the nut. What is the torque applied?

• 7.5 Nm

• 15 Nm

• 30 Nm

• 0.5 Nm

Which of the following factors does not affect torque?

• Magnitude of the force

• Distance from the pivot

• Angle of the force

• Mass of the object