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physics Physics For High Schools (KS4)

Solved problems for the chapter:

Moment of a Force

View the theory »

Torque

1. Calculation of torque

1.1. Calculation of torque using the component of force perpendicular to the distance

1.2. Calculation of torque using the component of the distance perpendicular to the force

2. Addition and subtraction of torques

3. Equilibrium and moment of forces

4. Spiral spring torque

5. Centre of gravity

5.1. Calculation of torque using the centre of gravity of a body

5.2. Centre of gravity of a system of point bodies

6. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:moment_of_a_force/3512/

Example 1.

What is meant by the moment of a force on an object?

The magnitude of the force on the object.
The direction of the force on the object.
The time for which the force acts on the object.
The turning effect of the force on the object.

Example 2.

Which statement about the moment of a force is not correct?

The moment of a force is the measure of its turning effect.
The moment of a force about a point increases when its perpendicular distance from the point from the point increases.
The moment of a force about a point is equal to: force x perpendicular distance from the point.
The moment of a force about a point increases when its perpendicular distance from the point from the point decreases.

A force acts on an object at a distance from a pivot. Which two changes both increase the moment of the force about the pivot?

	change 1	change 2
A	decrease	decrease
B	decrease	increase
C	increase	decrease
D	increase	increase

Two boys are sitting on a see-saw. The see-saw is equilibrium and remains horizontal as shown below.

Which of the following affects the moment of each boy about the pivot?

his distance from the pivot only
his height above the ground and his weight
his weight only
his weight and distance from the pivot

A beam is pivoted at P. A force is applied to the beam as shown below.

Which distance is multiplied by the force to give the moment of the force about P?

A rule is balanced at its mid-point. A force of acts at a distance of from one end of the rule as shown below.

Calculate the moment of the force about the pivot.

A force is applied to a spanner as shown below.

Which action increases the moment of about the centre of the nut?

apply the force to the end of the spanner handle
apply the force parallel to the spanner handle
spray oil on the nut
use a shorter spanner

An object is pivoted at point P. A student ties a length of string to a peg on the object. He pulls the string with a force as shown below.

What is the moment of the force about the point P?

The figure below shows a nut being turned with a spanner by applying a force to the spanner.

Which equation gives the moment of the force about the centre of the nut?

10.

The figure below shows a simple balance. The two loads, X and Y, can be moved along the beam.

Which of the graphs below shows how the moment produced by load Y varies as the perpendicular distance from the pivot changes?

11.

A beam pivoted at its centre of mass is acted upon by two forces and as shown in the figure below.

Calculate the resultant moment about the pivot.

clockwise
anticlockwise
clockwise
anticlockwise

12.

The diagram below shows a uniform metre rule that is pivoted at its centre and balanced by a box of weight and a ball of weight .

Which of the equations below about , , and is correct?

13.

Three uniform beams X, Y, and Z, each pivoted at its centre and acted upon by two forces are shown below.

Which beams rotate anticlockwise?

X and Y
X and Z
Y and Z
X, Y and Z

14.

A beam balance is as shown below.

The pivot is then moved to the right.

What will be the effect of this change on the clockwise and anticlockwise moments about the pivot?

	clockwise moment	anticlockwise moment
A	decrease	increase
B	increase	increase
C	increase	decrease
D	decrease	decrease

15.

The figure below shows the force applied to the brake pedal of a car by a driver's foot.

Calculate the moment of the force about the pivot.

16.

A car driver needs to remove one of the wheels on his car. He puts a spanner on a wheel nut and applies a force of a shown below.

Calculate the moment of the force about the centre of the wheel nut.

17.

A car driver needs to remove one of the wheels on his car. He puts a spanner on a wheel nut and applies a force of a shown below.

However, the moment produced by the force does not release the wheel nut. The driver cannot increase the force but can increase its moment. State and explain how the driver can increase the moment of the force.

18.

The figure below shows the force on a pulley from a load M (not shown).

The weight of load M is and the weight acts at a distance from the pivot of the pulley wheel. Calculate the moment of the weight of load M about the pivot.

19.

A student is doing some physical exercises. The figure below shows the student holding a weight.

The pivot in the shoulder is from the centre of mass of the weight. Calculate the moment of the weight about this pivot.

20.

The figure below shows the force acting on a uniform balanced beam. The beam is pivoted at its centre.

Calculate the moment of the force about the pivot.

21.

The figure below shows the handle used to open and close a cupboard door on the aeroplane.

A force of acts at a distance of from the pivot of the handle. Calculate the moment of the force about the pivot.