Work done & energy transfer

A wrench is used to turn a nut.

(Source: https://www.shutterstock.com/image-photo/adjustable-spanner-isolated-on-white-chrome-1794553030)

The force applied to the wrench is 28 N.

Calculate the moment applied by the wrench on the nut.

Give a suitable unit.

State two changes that could be made to increase the size of the moment applied to the nut.

Diagram 2 shows the wrench as it is turned through 90°

(Source: https://www.shutterstock.com/image-photo/adjustable-spanner-isolated-on-white-chrome-1794553030)

The force is applied over a distance that is equal to a quarter of the circumference of a circle.

The circle has a radius of 15 cm.

Calculate the distance over which the force is applied. [circumference of circle = 2πradius]

Calculate the work done by the force as the wrench is turned through a quarter of the circumference of the circle.

A model electric motor is used to lift a load through a vertical height.

The load has a mass of 400 g and gains 3.2 J of energy in its gravitational store when lifted.

State the formula linking gravitational potential energy, mass, gravitational field strength (g) and height.

Calculate the height the load is lifted.

State the amount of useful work done on the load by the motor when the load is lifted through this height.

The load is lifted at a constant speed.

Diagram 1 shows the lifting force acting on the load as it is lifted.

Draw a labelled arrow on diagram 1 to show the other force acting on the load.

Ignore the effects of air resistance.

Diagram 1

A joulemeter measures the amount of energy transferred electrically to the motor as the motor lifts the load.

The joulemeter displays a reading of 11.0 J when the load has gained 3.2 J of energy in its gravitational store.

Calculate the efficiency of the motor.

Justify why 7.8 J of energy must be dissipated into the thermal store of the surroundings as the load is lifted.

Diagram 2 is an incomplete Sankey diagram.

Complete the Sankey diagram to show the energy transferred by the motor.

A winch is used to pull a truck along a horizontal road.

The winch is connected to the truck by a thick rope.

The winch does 41 kJ of useful work on the truck when the truck is pulled a horizontal distance of 15 m.

State the formula linking work done, force and distance moved in the direction of the force.

Calculate the force that the rope exerts on the truck.

The winch includes a small engine. The engine burns petrol to power the motor in the winch.

The winch transfers energy mechanically to the truck.

The winch has an efficiency of 25% when pulling the truck.

Draw a Sankey diagram for this energy transfer.

The winch can also be used to pull the truck uphill at a constant speed.

The table gives some energy stores.

Add one tick () to each row to show what happens to the energy in each store as the truck is pulled uphill.

A teacher demonstrates the penetrating ability of alpha, beta and gamma radiation from some radioactive sources.

State a precaution the teacher should take to make sure they are working safely with the radioactive sources.

State the name of a detector the teacher could use to detect the radiation from each source.

Draw crosses () in the table to show which type of radiation cannot penetrate each material in the table.

An alpha particle of mass 6.610^–27kg travelling at a speed of 2.110⁷m/s hits a sheet of paper.

Calculate the kinetic energy (KE) of the alpha particle.

State the work done on the alpha particle when its speed is reduced to 0 m/s by the sheet of paper.

State which energy store of the paper increases when the alpha particle is stopped.

The photograph shows a toy car. When the toy car is pulled backwards, energy is stored in the elastic store as the rubber band is twisted.

(Source: Mama Belle and the kids/Shutterstock)

When the car is released, some of the energy from the elastic store is transferred to the kinetic store of the car.

The remaining energy is transferred into the thermal store of the surroundings.

State what is meant by the principle of conservation of energy.

The car is pulled backwards so that there is 165 J of energy in its elastic store.

When the car is released, this energy is transferred to the car’s kinetic energy store with an efficiency of 15 %.

State the formula linking efficiency, useful energy output and total energy output.

Calculate the energy transferred into the thermal store of the surroundings.

Draw a labelled Sankey diagram for this energy transfer.

The car is pulled backwards again.

When released, 45 J of energy transfers into the car’s kinetic store.

The car travels a distance of 7.5 m during this energy transfer.

State the useful work done on the car.

Calculate the mean accelerating force acting on the car.

The diagram shows a ball at the bottom of a ramp. The ball moves up the ramp with an initial speed v.

State the formula linking gravitational potential energy (GPE), mass, gravitational field strength (g) and height.

The ball has a mass of 14 g.

Show that when the ball reaches a height of 29 cm above the bottom of the ramp, the GPE gained by the ball is about 4 10⁻²J.

At the bottom of the ramp, the 14 g ball has a kinetic energy (KE) of 5.1 10⁻²J.

Calculate the speed of the ball at the bottom of the ramp.

The ball is stationary when it reaches the top of the ramp. There is a difference between the KE of the ball at the bottom of the ramp and the GPE of the ball at a height of 29 cm above the bottom of the ramp.

Explain why the work done by friction between the ball and the ramp is equal to this difference.

The photograph shows the Three Gorges Dam in China, one of the largest hydroelectric power stations on Earth.

State two advantages of generating electricity using hydroelectric power stations.

Water is held in a reservoir on one side of the dam.

The water flows through turbines to a river on the other side of the dam.

The water level of the river is lower than the water level of the reservoir.

State which energy store of the water decreases as the water flows from the reservoir to the river.

How is energy transferred from the dam to homes and factories in China?

The Three Gorges Dam has a larger maximum output power than any other hydroelectric power station on Earth.

State what is meant by the term power.

The mean energy transferred by the dam each day is 9.710¹⁴ J.

Calculate the mean output power of the dam.

The maximum output power is 22 500 MW.

Which of these is the same as 22 500 MW?

Suggest why the Three Gorges Dam does not always operate at its maximum output power.

A student uses this apparatus to investigate the force needed to pull a block along a ramp.

State the formula linking work done, force and distance moved in the direction of the force.

The student pulls the block 0.89 m along the ramp with a force of 26 N.

Show that the work done on the block by the 26 N force is about 23 J.

The block has a mass of 1.3 kg and moves vertically upwards 0.11 m.

Calculate the increase in the gravitational potential energy (GPE) store of the block between the bottom and the top of the ramp.

Explain why the work done to move the block along the ramp is greater than the increase in the GPE store of the block.

The student suggests it is better to use a less steep ramp to raise the block through the same vertical height.

Discuss an advantage and a disadvantage of using a less steep ramp.

State Hooke’s Law.

The graph shows how the extension of a rubber band varies with the force applied.

Explain how the graph shows that the rubber band does not obey Hooke’s Law.

Diagram 1 shows a model aeroplane powered by a rubber band.

A person rotates the propeller of the model aeroplane, which twists the rubber band.

He then releases the propeller and it spins.

Energy transfer occurs during this process.

The box lists words associated with energy.

Use words from the box to complete the passage.

The person does_........ work to twist the rubber band.

As the person twists the rubber band it extends, increasing the_........

energy store of the rubber band. When the rubber band is released it does mechanical work,

increasing the_........ energy store of the propeller.

Diagram 2 shows the aeroplane flying horizontally to the right.

Diagram 2

The aeroplane flies at a constant speed.

Diagram 2 shows two forces acting on the aeroplane.

Draw labelled arrows on diagram 2 to show two more forces acting on the aeroplane.

The photograph shows a device that can be used to ignite small pieces of combustible material.

The device consists of a cylinder containing trapped air and a piston.

A small piece of combustible material is placed at the bottom of the cylinder.

When the piston is pushed quickly into the cylinder, the trapped air is compressed and heats up.

This increase in temperature is enough to ignite the combustible material.

The piston is quickly pushed down a distance of 145 mm.

The average force exerted on the piston is 4.2 N.

State the formula linking work done, force and distance moved in the direction of the force.

Calculate the work done on the trapped air when the piston is quickly pushed down.

State the maximum amount of energy that could be transferred to the trapped air.

Using ideas about molecules, explain why the trapped air heats up.

Suggest why the trapped air does not reach a high enough temperature to ignite the combustible material if the piston is slowly pushed into the cylinder.