Forces

Newton’s third law describes two quantities that are equal in magnitude and opposite in direction. What unit is used for these two quantities?

May/June 2015

A force is applied to a body. Which list contains only quantities that the force can alter?

May/June 2016

In the diagram, the resultant $R$ of a $3.0\,\text{N}$ force and a $4.0\,\text{N}$ force applied at a single point is shown. The angle separating the $3.0\,\text{N}$ force and the $4.0\,\text{N}$ force may take any value from $0^\circ$ to $90^\circ$. Which value of $R$ cannot occur?

May/June 2017

The diagram illustrates the resultant $R$ produced by two forces of $3.0\,\text{N}$ and $4.0\,\text{N}$ applied at one point. The angle between the $3.0\,\text{N}$ force and the $4.0\,\text{N}$ force may take any value between $0^{\circ}$ and $90^{\circ}$. Which value of $R$ cannot occur?

May/June 2017

A train with a mass of $240\,000\,\text{kg}$ is moving at $60\,\text{m s}^{-1}$. When the brakes are used, it slows down for $10\,\text{minutes}$ before stopping completely. What is the average resultant force?

May/June 2017

Two forces, $4.0\,\text{N}$ and $2.0\,\text{N}$, act at a point. Which scale diagram represents the forces whose resultant is $4.0\,\text{N}$?

May/June 2018

A student is examining the upward force acting on a cylinder in water. Before the cylinder is put into the water, he hangs it from the end of a newton meter, as illustrated in Fig. 3.1.

May/June 2019

An object is acted on by a force of $3.0\,\text{N}$ and another force of $4.0\,\text{N}$. What is the greatest possible resultant of these two forces?

May/June 2022

Two forces of $6.0\,\text{N}$ and $8.0\,\text{N}$ act in the arrangement shown. Which diagram illustrates the resultant $R$ of these two forces?

May/June 2023

What is the magnitude of the resultant of the two forces shown?

May/June 2023

Newton’s third law refers to a pair of forces. Which row indicates whether the two forces are the same type and whether they act on one object?

May/June 2023

A student fixes a propeller to an electric motor that is powered by a $0$ to $12\,\text{V}$ d.c. power supply, as shown in Fig. 4.1. The air set in motion by the propeller exerts a force on the balance. Plan an experiment to investigate how this force changes with the voltage of the power supply. The apparatus available is: an electric motor, an electronic balance, a power supply, a propeller, a voltmeter. You may also use other apparatus and materials that are normally found in a school laboratory.

May/June 2023

An object moves down a frictionless slope, as illustrated. When the object exerts a force on the surface, the surface exerts a force on the object in return. In which direction does the surface exert this force on the object?

May/June 2024

The four gravitational forces acting between objects in the Solar System are given below. P: the force on the Moon due to the Earth. Q: the force on the Earth due to the Sun. R: the force on the Earth due to the Moon. S: the force on the Moon due to the Sun. Which two forces form a Newton’s third law pair?

May/June 2024

A force acts on a body. Which properties of the body might all be altered by the force?

Oct/Nov 2015

Each diagram illustrates two forces with the same magnitude. Which diagram shows two forces that form a Newton’s third law pair?

Oct/Nov 2016

A man who has an open parachute is descending towards Earth at constant speed. The forces acting are shown below. P: the upward force exerted by the parachute on the man. Q: the upward force exerted by the man on the Earth. R: the downward force exerted by the Earth on the parachute. S: the downward force exerted by the man on the parachute. Which two forces form a Newton’s third law pair?

Oct/Nov 2016

Fig. 9.1 depicts an astronaut in space close to a space station orbiting above the Earth. The astronaut plus all of his equipment has a total mass of 160 kg. At first the astronaut is stationary relative to the space station, then the rope pulls him towards the space station. His acceleration towards the space station is $0.35\,\text{m s}^{-2}$ for 1.2 s.

Oct/Nov 2017

Which diagram illustrates the addition of the $4.0\,\text{N}$ force and the $3.0\,\text{N}$ force?

Oct/Nov 2018

Which diagram illustrates the addition of the $4.0\,\text{N}$ force and the $3.0\,\text{N}$ force?

Oct/Nov 2018

A body slides down a slope with no friction, as shown. As the body exerts a force on the surface, the surface exerts a reaction force on the body. In what direction does this reaction force act on the body?

Oct/Nov 2019

A body moves down a frictionless slope, as shown. As the body is in contact with the surface, the surface exerts a force on the body. In which direction is this force acting?

Oct/Nov 2019

Which list includes only quantities that can be changed by a force?

Oct/Nov 2020

Which list includes only quantities that a force can alter?

Oct/Nov 2020

A man is stationary on the Earth's surface. The man's weight is the gravitational force acting on him. By Newton's third law, the man's weight is one force in an action-reaction pair. Which force forms the other member of the pair?

Oct/Nov 2025

An object is acted on by two forces. One force of $1.5\text{ N}$ acts vertically upward and another force of $2.0\text{ N}$ acts horizontally. What is the magnitude of the resultant force?

Oct/Nov 2025