Work done & energy transfer

A student went on a cycling journey that lasted for three days.

The student recorded information about the journey using a cycling app on a mobile phone.

At the start of the journey, the student travelled along a straight road to a road junction.

A map on the cycling app showed the road.

Figure 5 shows the map.

The scale of the map is 1 cm: 20 m

Calculate the distance travelled by the student between the start and the

road junction.

Use Figure 5.

The bicycle had a mass of 15 kg.

gravitational field strength = 9.8 N/kg

Calculate the weight of the bicycle.

Use the equation:

weight = mass × gravitational field strength

Figure 6 shows a velocity–time graph for a downhill part of the journey.

The gradient of the graph represents acceleration.

How does Figure 6 show that the acceleration was constant?

As the student accelerated downhill, the forward force on the student was 250 N.

The work done by the forward force was 4500 J.

Calculate the distance travelled as the student accelerated downhill.

Use the equation:

Most of the roads on the journey were not straight.

Figure 7 shows a map of the route taken for the whole journey.

The line in Figure 7 represents the total distance travelled when the student reached the end of the journey.

How does the total distance travelled compare with the magnitude of the displacement of the student from the start?

Tick () one box.

Why is distance a scalar quantity?

Tick () one box.

Figure 8 shows the distance travelled by the student each day.

Calculate the total distance travelled by the student.

Use Figure 8.

A triathlon race consists of swimming, cycling and running.

One athlete in a triathlon swims at a speed of 1.5 m/s.

How does the athlete’s swimming speed compare with the typical speed of a person walking?

Tick () one box.

Figure 8 shows a speed–time graph for the athlete for the whole triathlon.

The cycling part of the race was on a straight road.

The work done by the forward force on the bicycle was 110 000 J.

Determine the mean forward force on the bicycle.

Use the Physics Equations Sheet.

Figure 8 is repeated below.

The first part of the run was on a circular track.

The time taken for the athlete to run round the track was 100 s.

Describe the velocity of the athlete during the first 100 s of the run.

Use Figure 8.

After running round the track once, the rest of the run was on a straight, horizontal road.

Explain how Figure 8 shows that the magnitude of the deceleration of the athlete increased.

The stopping distance of a car depends on the thinking distance and the braking distance.

Which of the following affects the thinking distance?

Tick () one box.

A car manufacturer tested three different types of tyre which were fitted to three identical cars.

This is the method used.

1. Drive the car along a road.

2. Apply the brakes until the car stops.

3. Measure the distance travelled while braking.

4. Repeat steps 1 to 3 for each car when the road is dry and when the road

is wet.

The brakes were applied with the same force for each test.

Give one other variable that should have been kept the same for each test.

Figure 10 shows the results.

The manufacturer wants to put the safest tyres on a new car.

Evaluate the safety of each type of tyre.

Use data from Figure 10.

When the brakes are applied, a force does work to stop the car.

Use the Physics Equations Sheet to answer questions 05.4 and 05.5.

Write down the equation that links distance (s), force (F) and work done (W).

The braking force acting on a car is 6000 N.

The work done to stop the car is 300 000 J.

Calculate the braking distance of the car.

Explain how the force applied by the brakes affects the braking distance of the car.

Figure 13 shows an engineer climbing up a ladder.

The distance between each rung on the ladder is 30 cm.

What is 30 cm in metres? Tick (✓) one box.

The engineer has a weight of 710 N. Calculate the work done when climbing up one rung of the ladder. Use your answer to Question 05.1 and the equation: work done = force × distance

The engineer climbs the ladder carrying some equipment. Give the reason why carrying equipment increases the work done by the engineer when climbing the ladder.

The engineer is stationary at the top of the ladder. Which energy stores of the engineer increase due to the engineer climbing the ladder? Tick (✓) two boxes.

Use the Physics Equations Sheet to answer questions 05.5 and 05.6.

Write down the equation that links gravitational field strength (g), mass (m) and weight (W).

The engineer has a weight of 710 N. gravitational field strength = 9.8 N/kg Calculate the mass of the engineer. Give your answer to 2 significant figures.

Figure 10 shows competitors in the wheelchair race at the London Marathon. The distance of the London Marathon is 42 000 m

Use the Physics Equations Sheet to answer questions 07.1 and 07.2.

Write down the equation that links distance (s), force (F) and work done (W).

During the race competitors work against air resistance. The work done against air resistance by the winner of the race was 3 360 000 J Calculate the average air resistance acting on the winner of the race.

Use the Physics Equations Sheet to answer questions 07.3 and 07.4.

Which equation links distance travelled, speed and time? Tick (✓) one box.

The distance of the London Marathon is 42 000 m The winning time for the race was 5600 seconds. Calculate the average speed of the winner of the race.

Explain why the speed of a competitor changes during the race.

Figure 3 shows competitors in the wheelchair race at the London Marathon. The distance of the London Marathon is 42 000 m

Use the Physics Equations Sheet to answer questions 02.1 and 02.2.

Write down the equation that links distance (s), force (F) and work done (W).

During the race competitors work against air resistance. The work done against air resistance by the winner of the race was 3 360 000 J Calculate the average air resistance acting on the winner of the race.

Use the Physics Equations Sheet to answer questions 02.3 and 02.4.

Which equation links distance travelled, speed and time? Tick (✓) one box.

The distance of the London Marathon is 42 000 m The winning time for the race was 5600 seconds. Calculate the average speed of the winner of the race.

Explain why the speed of a competitor changes during the race.

Scientists are developing a rocket aeroplane designed to travel much faster than jet aeroplanes.

The rocket aeroplane must accelerate along a runway to take off.

What would happen to the air resistance acting on the rocket aeroplane as it accelerates?

During the first 14 seconds the average speed of the rocket aeroplane on the runway will be 35 m/s.

Calculate the distance that the rocket aeroplane will travel during the first 14 seconds.

Use the equation:

distance travelled = average speed × time

Write down the equation which links distance (s), force (F) and work done (W).

When the rocket aeroplane travels a distance of 270 m on the runway the engines will do 54 000 000 J of work.

Calculate the average force exerted by the engines.

The rocket aeroplane will fly at a greater height than a jet aeroplane.

The height that an aeroplane flies at affects the radiation dose a passenger will receive each hour.

Table 2 shows the speed of each aeroplane and the radiation dose a passenger will receive each hour.

Exposure to ionising radiation has risks and possible consequences.

Evaluate the risks and possible consequences of flying in a rocket aeroplane and in a jet aeroplane.

Assume the same journey is made in each aeroplane.

Use values from Table 2.

Different parts of the electromagnetic spectrum are used in medical imaging. Figure 8 shows an image of a person’s hand taken with an infrared camera.

Explain why the infrared camera is able to show that parts of the hand are at different temperatures.

Infrared has a range of wavelengths from 700 nm to 1 mm. Which part of the electromagnetic spectrum would have waves with a wavelength of

Tick (✓) one box.

Figure 9 shows X-rays and gamma rays being used for medical imaging.

Figure 9

To use X-rays for medical imaging, a machine produces a very brief burst of X-rays. To use gamma rays for medical imaging, a radioactive isotope is injected into the patient’s blood. The isotope is circulated around the body in the blood. The isotope emits gamma rays.

Compare the potential risks to a patient of using X-rays and gamma rays for medical imaging.

X-rays are produced by colliding high-energy electrons into a metal target. The electrons have high energy because they are accelerated to high speeds. Only a small proportion of the kinetic energy of an electron is converted into an X-ray when it collides with the metal target.

An electron is accelerated through a distance of 15 mm. The work done on the electron is 1.2 × 10^–13 J. Calculate the force on the electron.

The metal target is made from tungsten. Tungsten has the highest melting point of any metal. Explain why using tungsten as the metal target enables the X-ray machine to be more powerful.

Figure 5 shows a distance-time graph for 50 seconds of a bicycle ride.

The gradient of the distance-time graph gives the speed of the bicycle. Determine the speed of the bicycle.

Which force acting on the moving bicycle is a non-contact force? Tick (✓) one box.

The bicycle travels a distance of 250 m The bicycle exerts a constant horizontal force of 30 N on the ground. Calculate the work done. Use the equation: work done = force × distance Choose the unit from the box.

The bicycle travels at a constant speed. Complete the sentences. Choose answers from the box.

The thinking distance of a car depends on the reaction time of the driver.

Figure 6 shows how thinking distance varies with reaction time for a car travelling at 30 m/s

The reaction time of a driver can double if the driver is distracted.

Explain the effect doubling the reaction time has on the thinking distance.

Use data from Figure 6.

Give the reason why there are no values of thinking distance for reaction times less than 200 milliseconds.

A driver measured her reaction time using an online test. She did the test five times.

Table 2 shows the results.

How does the data in Table 2 show that it was important that the driver did the test five times?

Calculate the mean reaction time of the driver.

The driver is driving her car at 30 m/s

Determine the thinking distance.

Use Figure 6 and your answer from Question 04.4

The driver applies the brakes and the car comes to a stop.

The force exerted by the brakes affects the braking distance.

Give two other factors that affect the braking distance.

Write down the equation that links distance, force and work done.

When the driver applies the brakes, there is a constant resultant force of 6.0 kN on the car.

The car travels a distance of 75 m before stopping.

Calculate the work done in stopping the car.

Figure 4 shows a man doing two stages of a pull up. In both diagrams the man is stationary.

Complete the sentence.

Choose the answer from the box.

upwards force of the bar on the man.

The man has a mass of 85 kg

Gravitational field strength = 9.8 N/kg

Calculate the weight of the man.

Use the equation:

weight = mass × gravitational field strength

The man raises his body a vertical distance of 0.63 m to go from stage 1 to stage 2

Calculate the work done by the man.

Use your answer to question 03.2

Use the equation:

work done = force × distance

The man was not moving at stage 2 How much work is done by the man at stage 2?

A woman uses the bar to do a pull up.

The woman has a mass of 62 kg

Calculate the resultant force on the woman.

Use the equation:

force = mass × acceleration