4.2 Work, Power & Energy Resources

A student has a bicycle with a dynamo (generator) that supplies electricity for its lights. The friction wheel, W, presses against the bicycle tyre. When the student pedals, the friction wheel turns and causes part Y to rotate.

Calculate the total useful energy output.

In 2013, the UK Government decided to build another nuclear power station at Hinckley Point.

Hinckley Point is in Somerset, a major agricultural area of the UK.

This is the third nuclear power station at the site. 

The table gives information about some ways to generate electrical power.

An electricity supply company has enough power stations to cover the normal demand for electricity but not enough for cold conditions. On cold days the demand for electrical power can suddenly increase by 20 000 MW.
The company needs to build new power stations to meet this increased demand. 

Using only information in the table, evaluate which types of power station would be the most suitable to meet this increased demand.

An energy company plans to build a new power station. The company must decide between two renewable energy projects, a geothermal power station or a solar power station.

Explain how the location and the climate might affect the type of power station that the company chooses.

The photograph shows a type of rollercoaster.

The car is launched from point A in the photograph, accelerates to point B and then rises over point C.

Each loaded car has a mass of 2000 kg.

C is 128 m above B.

The car gains kinetic energy when work is done on it by the launching system between A and B.

Assume there are no energy losses.

Sometimes the car does not reach C, but rolls backwards to the start.

This can happen when it becomes windy or the track becomes wet.

Explain why these conditions could cause the car to stop before it reaches C.

In 1971, astronaut Alan Shepard hit a golf ball on the surface of the Moon.

The golf ball had a mass of 50 g and he transferred 56 J of energy to it. 

At its highest point the ball had gained 12 J of gravitational potential energy.

Suggest why the ball travelled further on the Moon than it would have done on Earth.

The diagram shows a motor lifting a 130 g mass.

The current in the motor is 2.1A and the voltage across it is 12 V. The motor takes 1.5 s to lift the mass.

An underground train enters a station.

The mass of the train and its passengers is 250 000 kg.

The total kinetic energy is 18 MJ.

The diagram shows a section through the station.

A student investigates how the energies of a ball and spring change when the ball and spring vibrate together.
The diagrams and bar charts show how the energies of the ball and spring vary with the position of the ball.

The ball has a mass of 1 kg.

A person has a suitcase with wheels.

The person pulls the suitcase with a horizontal force of 13 N for 110 m.

The suitcase falls over.

Explain why it loses gravitational potential energy when it falls.

The photograph shows equipment used for generating electricity from renewable sources.

On a windy day, the wind turbine transfers 78 W of power.

A man uses a wheelbarrow to carry some logs along a flat path, as shown.

State the relationship between work done, force and distance moved. 

Supermarkets use conveyer belts to move shopping at the till. The diagram shows a carton of milk being pulled along by a horizontal conveyer belt.

The horizontal force on the carton from the belt is 1.7 N. The carton moves a distance of 0.46 m. 

State the equation linking work done, force and distance.

The photograph shows a machine at a coal mine.

^{© Andrew Curtis}

The machine lifts a load weighing 400 000 N through 190 m.

The machine uses an average (mean) power of 1.9 MW to do 67 MJ of work.

A flying squirrel is an animal that can glide through the air. It spreads out its limbs to stretch out a membrane that helps it to glide. 

^{© Robert Savannah}

The mass of a flying squirrel is 0.19 kg. It climbs 17 m up a tree.

The flying squirrel glides from P to Q with a velocity of 13 m/s.

A resistance band is a stretchy plastic band that is used when doing exercises. The diagram shows a student exercising his leg by stretching a resistance band fixed to a wall.

The student moves his leg 34 cm sideways as shown. The average resistance force is 23 N.

(1)

The student repeats this movement 15 times in 1 minute. Calculate the average power of the student during this exercise.

A shopping centre has escalators to move people between floors.

A man of mass 78 kg steps on to an escalator. The escalator lifts him a height of 5.0 m. 

State the equation linking gravitational potential energy, mass, g and height.

A student investigates the energy transfers in a small generator. She connects the generator to a circuit that includes a lamp. She hangs a mass from a string wound around the axle. The lamp lights as the mass falls to the ground.

The table shows the student’s results.

The car pulls the caravan with a resultant force of 170 N for a distance of 110 m. 

The mass of the car is 1650 kg. 

The mass of the caravan is 950 kg. 

 Total kinetic energy = .................J

The diagram shows a roller-coaster ride. The car is pulled slowly from the start to point B and then released.

Choose letters from the diagram to complete this sentence.

The car has the most gravitational potential energy at point ........................... and it goes fastest at point ......................... .

The mass of the car is 900 kg. The maximum speed of the car is 15 m/s.

A coal-fired power station and a wind turbine both produce electrical power. The power station produces 1200 MW and the wind turbine produces 1.5 MW.

Give one advantage of using wind turbines instead of a coal-fired power station to produce electricity.

Coal-fired power stations are still in general use.

Explain why wind turbines have not replaced them.

Some energy sources are renewable and other energy sources are non-renewable.

The photograph shows a wind farm that generates electricity for the National Grid.

A ball has a mass of 0.25 kg. A student holds the ball 1.75 m above the ground.

The student lets the ball fall.

State the value of the kinetic energy (KE) of the ball just before it hits the ground.

Assume that there is no air resistance. 

KE = ........................... J

Another ball with the same mass has a kinetic energy of 3.1 J.