AP Physics 1 · Unit 5 · Rotation

Torque Practice Problems

Work from a force diagram to its turning effect about a named axis. Compare door pushes, resolve an angled fishing-line pull, add three wheel torques, change a beam’s pivot, and calculate gravity torque on a pendulum.

13 questions6 conceptual · 7 calculation

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Simulation scene from the Torque lesson. — A scene from the related lesson. Open the practice to work through the questions.

What you’ll practice

Choose the axis and find the perpendicular geometry

Connect force, distance, and angle

Compare a push at a door’s center with one at its outer edge. Find the force needed for a target torque and use the angle between the position vector and force, rather than an unrelated diagram angle.

Add turning effects about a common axis

Assign clockwise and counterclockwise signs before adding wheel torques. Calculate the same three beam forces about two axes and identify which forces have zero moment about each one.

Construct a perpendicular lever arm

Use either rF sin θ or Fd for a fishing rod and a small mounting tab. For a pendulum, identify the horizontal lever arm of its vertical weight and keep the angle measured from vertical.

A question from this set

Same push, different distance

The same perpendicular force is applied to a rigid door first at distance r from its hinge, then at distance 2r. What happens to the torque magnitude about the hinge?

It stays the same because the force is unchanged.
It doubles.
It becomes four times as large.

Try it in the practice set

The same perpendicular push acts at two distances from a hinge. Compare the turning effect about the marked pivot.

Key ideas

Force magnitude alone does not determine torque

A lever arm is measured to a line of action

The perpendicular distance from the pivot to the force’s line of action determines the turning effect. A large force can produce zero torque when that line passes through the pivot.

The axis and turning signs matter

Equal opposite forces can form a couple with zero net force and nonzero torque. Moving the reference axis can change a force’s moment arm and even reverse its torque sign.

See the physics

Inspect starting geometry and subsequent motion

After attempting a question, run the prepared bar, wheel, or pendulum. Compare each force’s starting moment with the recorded net torque, switch beam pivots, and inspect the changing torque when a fixed-direction force acts on a rotating bar. A magnified view keeps the mounting tab’s centimeter-scale geometry visible.

Use a hint for a starting point or open a worked solution to follow the reasoning. Your progress saves in this browser, so you can return to unfinished questions.

Ready for torque?

Begin with a conceptual question, then work through the calculations.

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