TP1 Energy

Aim: The aim of this unit is to go back through some key concepts of energy including energy transformations, the conservation of energy and some important calculations which you will need to be able to perform in your exams. This unit covers calculating work, gravitational potential energy, and kinetic energy.

Introduction

James Prescott Joule was born in Salford Lancashire in 1818 and he is considered to be the “father of Energy”. He was a Physicist and mathematician. In the scientific world he is most remembered for his work on heat and mechanics where he defined the “First law of thermodynamics” and the “Conservation of Energy”.

Key Words and Meanings

Key Concepts

The conservation of energy:
“Energy cannot be created or destroyed but only changed from one form to another.”

Work:
When an object is moved by a force work is done.

Work = Force x distance moved
Kinetic energy = 1/2 Mass x Velocity²
Gravitational Potential Energy = mass x gravitational field strength x height change

All energy is measured in Joules. This is very important to remember.

Revision questions on the conservation of energy

1. describe the energy changes involved when switching on a light, and represent your answer as a flow chart.
2. Potential energy is usually stored energy, what does this mean?
3. When energy is transferred, explain what we mean by Useful, Wasted and Dissipated.
4. Why does a swinging pendulum eventually come to rest (stop swinging) if left alone?

Video showing answers to questions on the Conservation of energy

Revision questions on Work

1. state the equation used to calculate work done.
2. How much work would you do pushing a wheel barrow loaded with 30kg of bricks 25m?
3. If a girl carries a pile of books for 8 seconds at a steady speed of 2m/s, using a force of 95N, how far did she travel and how much work did she do?
4. A girl of mass 50kg climbs up a tree to a height of 9m. Calculate the weight of the girl and how much work she did climbing up the tree.

Video showing answers to questions on work done

Revision questions on Kinetic energy

1. State the formula used to calculate kinetic energy and explain what kinetic energy is.
2. A boy of mass 65 kg is running at 7 m/s, calculate his kinetic energy.
3. A car of mass 1800kg comes to a sudden stop when the brakes are applied. if the energy required by the brakes is 190,000 joules, how fast was the car moving just before the brakes were applied?
4. A lorry is moving at 32 m/s on a road. It has 1.5 million joules of kinetic energy, what is the lorries mass? (assume no energy is lost to the surroundings, ie a closed system)

Video showing answers to the questions on Kinetic energy

Revision questions on Gravitational potential energy

1. What is the difference between mass and weight?
2. Explain why an objects GPE changes depending upon where it is.
3. A tennis ball is thrown up into the air. If the tennis ball has a mass of 57g and reaches a height of 20m, how much GPE does it have at this point? (g=9.8 N/kg)
4. A golf ball of mass 50g is hit 30m up into the air, when it falls back to the ground, it bounces 6m in height initially. Calculate the difference in gravitational potential energy the ball has at each height and suggest why there is a difference. Assume g= 9.8 N/kg.

Video showing answers to Gravitational Potential energy (GPE) questions

\[\LARGE F=\frac{m\Delta v}{T}\]