Q: A force of 20 N is applied perpendicular to a wrench at a distance of 0.3 m from the pivot. What is the magnitude of the torque?

$\tau = 6.0\ \mathrm{N \cdot m}$

Q: A 2 N force is applied at the midpoint of a 1 m long rod pivoted at one end. What is the torque about the pivot?

$\tau = 2\ \mathrm{N} \times 0.5\ \mathrm{m} = 1\ \mathrm{N \cdot m}$

Q: A 90 N force is applied downward at the end of a wrench that is 0.5 m long, at an angle of $19^\circ$ to the lever arm. What is the magnitude of the torque?

$\tau = 0.5 \times 90 \times \sin 19^\circ$

Q: A rod is pivoted at one end. A 4 N force is applied at a distance $\dfrac{L}{2}$ from the pivot. What is the torque?

$\tau = 4N \times \dfrac{L}{2}$

Question 1

Which of the following best describes the physical meaning of torque ($	au$) in rotational motion?

Accepted Answer

Torque is the product of force and the perpendicular distance from the axis of rotation.

Question 2

A mechanic uses a wrench to loosen a bolt. If he applies a force $F$ at a distance $r$ from the pivot, what is the formula for the magnitude of the torque produced?

Accepted Answer

$	au = F 	imes r$

Question 3

You are trying to open a stuck door by pushing with a force of 10 N. Which position will produce the greatest torque?

Accepted Answer

Pushing at the edge farthest from the hinge with the force perpendicular to the door.

Question 4

A seesaw is balanced when:

Accepted Answer

The torques on both sides are equal in magnitude and opposite in direction.

Question 5

A force of 20 N is applied perpendicular to a wrench at a distance of 0.3 m from the pivot. What is the magnitude of the torque?

Accepted Answer

$	au = 6.0\ \mathrm{N \cdot m}$

Question 6

If two equal forces are applied to a wheel at equal distances from the center but in opposite directions, what happens to the net torque?

Accepted Answer

The net torque is zero.

Question 7

A person uses a pipe to extend the handle of a wrench. If the force applied remains the same, what happens to the torque?

Accepted Answer

The torque increases.

Question 8

Which of the following scenarios will result in zero torque about the pivot point?

Accepted Answer

A force is applied parallel to the lever arm at any distance from the pivot.

Question 9

A 2 N force is applied at the midpoint of a 1 m long rod pivoted at one end. What is the torque about the pivot?

Accepted Answer

$	au = 2\ \mathrm{N} 	imes 0.5\ \mathrm{m} = 1\ \mathrm{N \cdot m}$

Question 10

In the context of human anatomy, why is the hip joint particularly vulnerable to fractures in the elderly?

Accepted Answer

Because the torque generated by the pelvis on the femur can be very large due to high forces and lever arms.

Question 11

A force $F$ is applied at an angle $	heta$ to a lever arm of length $r$. What is the general formula for the magnitude of the torque?

Accepted Answer

$	au = F r \sin 	heta$

Question 12

A 90 N force is applied downward at the end of a wrench that is 0.5 m long, at an angle of $19^\circ$ to the lever arm. What is the magnitude of the torque?

Accepted Answer

$	au = 0.5 	imes 90 	imes \sin 19^\circ$

Question 13

If the kneecap is removed, what happens to the torque produced by the tendon pulling on the tibia?

Accepted Answer

The torque decreases.

Question 14

Why do animals have kneecaps from a physics perspective?

Accepted Answer

To increase the lever arm and thus the torque produced by muscles, allowing for faster leg movement.

Question 15

A rod is pivoted at one end. A 4 N force is applied at a distance $\dfrac{L}{2}$ from the pivot. What is the torque?

Accepted Answer

$	au = 4N 	imes \dfrac{L}{2}$

Question 16

Which of the following statements is true regarding the sign of torque?

Accepted Answer

A negative sign indicates clockwise rotation, depending on the chosen convention.

Question 17

A wheel is mounted on a fixed axle and two equal-magnitude forces are applied at opposite points on the rim, both perpendicular to the radius but in opposite directions. What is the resulting motion?

Accepted Answer

The wheel will not rotate because the torques cancel.

Question 18

A student applies a force at a point on a lever arm that is not perpendicular to the lever. How should the torque be calculated?

Accepted Answer

By using only the component of the force perpendicular to the lever arm: $	au = F r \sin 	heta$

Torque and Rotational Motion: Physics Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards