Question 1

What is the difference between work and energy?

Accepted Answer

Work is the process of transferring energy when a force moves an object. Energy is the capacity to do work. When work is done, energy is transferred from one store to another. For example, when you lift a book, you do work against gravity, and chemical energy in your muscles is transferred to gravitational potential energy of the book. The amount of work done equals the amount of energy transferred.

Question 2

How do you calculate work done when the force is at an angle?

Accepted Answer

When the force is at an angle to the direction of motion, you only use the component of the force that acts in the direction of motion. This component is F × cos(θ), where θ is the angle between the force and the direction of motion. So work done = F × cos(θ) × distance. For example, if you pull a sled with a rope at 30° to the horizontal, the horizontal component of the force does the work.

Question 3

What is the formula for power and how is it related to work?

Accepted Answer

Power is the rate at which work is done, calculated as power (watts) = work done (joules) / time taken (seconds). So if you do 100 J of work in 5 seconds, your power is 20 W. Power tells you how quickly energy is transferred. A more powerful machine does the same amount of work in less time. For example, a 100 W light bulb transfers 100 J of electrical energy into light and heat every second.

Question 4

Why is no work done when you push against a wall?

Accepted Answer

Work is defined as force × distance moved in the direction of the force. When you push against a wall, the wall does not move (distance = 0), so no work is done on the wall. However, your muscles are still using energy because they are contracting and generating heat, but that energy is not being transferred to the wall as work. Instead, it is wasted as thermal energy.

Question 5

How do you calculate work done against gravity?

Accepted Answer

Work done against gravity when lifting an object is equal to the weight of the object (mass × gravitational field strength, g) multiplied by the vertical height lifted. So work = m × g × h. For example, lifting a 2 kg mass 1.5 m high (with g = 9.8 N/kg) requires work = 2 × 9.8 × 1.5 = 29.4 J. This work is stored as gravitational potential energy.

Question 6

What is the difference between work done and energy transferred?

Accepted Answer

In physics, when work is done on an object, energy is transferred to that object. The amount of work done is exactly equal to the amount of energy transferred (assuming no energy is lost to the surroundings). So if you do 50 J of work lifting a box, the box gains 50 J of gravitational potential energy. However, in real situations, some energy is often wasted as heat due to friction, so the useful energy transferred may be less than the work done.

Topic 8 – Energy - Forces doing work

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Likely Command Words

Ready to test yourself?

Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 8 – Energy - Forces doing work — Edexcel GCSE Physics

Examiner Tips for Topic 8 – Energy - Forces doing work

Common Mistakes in Topic 8 – Energy - Forces doing work

Key Marking Points