Conservation & dissipation of energy

Figure 7 shows two people wearing inflatable bodysuits.

The bodysuits are made of soft plastic and are inflated with air.

The bodysuits reduce the chance of injury in a collision.

Explain how wearing a bodysuit reduces the chance of injury in a collision.

Figure 8 shows person A about to collide with person B.

The arrows show the direction in which each person is moving.

The velocity of person A is + 2.0 m/s.

The two people collide and stop.

Calculate the velocity of person B before the collision.

Use the Physics Equations Sheet.

Figure 9 shows a person in an inflatable sphere rolling down a hill.

The total mass of the person and sphere is 80 kg.

The sphere moves through a vertical height of 6.4 m.

gravitational field strength = 9.8 N/kg

Calculate the maximum possible speed of the sphere at the bottom of the hill.

Use the Physics Equations Sheet.

The actual speed of the sphere at the bottom of the hill is much less than the maximum possible speed.

Explain why.

Figure 5 shows a person driving a bumper car at a theme park.

The mass of the bumper car and driver is 360 kg.

The bumper car moves with a speed of 1.50 m/s.

Calculate the kinetic energy of the bumper car and driver.

Use the equation:

kinetic energy = 0.5 × mass × (speed)²

Use the Physics Equations Sheet to answer questions 06.2 and 06.3.

Write down the equation which links efficiency, total power input and useful power output.

The motor of the bumper car has an efficiency of 0.80

The total power input to the motor is 220 W.

Calculate the useful power output of the motor.

The bumper car collides with a stationary barrier and stops.

What happens to the velocity of the bumper car during the collision?

Figure 17 shows a desk lamp connected to the mains electricity supply.

The desk lamp is fitted with a high-efficiency LED bulb.

What does ‘high-efficiency’ mean?

Tick (✓) one box.

A large proportion of the total energy input is destroyed.

A large proportion of the total energy input is usefully transferred.

A large proportion of the total energy input is wasted.

The LED bulb wastes energy as thermal energy.

How does the thermal energy affect the temperature of its surroundings?

The output power of the lamp is 2.8 W.

Calculate the energy transferred by the lamp in 60 seconds.

Use the equation:

energy transferred = power × time

Mains electricity can be dangerous.

Table 2 shows information about the effects of different electrical supplies on the human body.

ac is alternating current.

Compare the effects on the human body of 50 Hz ac with 10 000 Hz ac.

Use data from Table 2.

Ten-pin bowling is a game where a ball is rolled along the floor to knock over some wooden pins.

Figure 1 shows a person ten-pin bowling.

The speed of the ball was 8.0 m/s just after leaving the person’s hand.

The mass of the ball was 5.5 kg.

Calculate the kinetic energy of the ball.

Use the equation:

kinetic energy = 0.5 × mass × (speed)²

When the ball collides with the pins, energy is conserved.

What is meant by ‘conservation of energy’ when the ball collides with the pins?

Tick (✓) one box.

The gravitational potential energy of the pins is the same before and after the collision.

The kinetic energy of the ball is the same before and after the collision.

The total energy of the ball and pins is the same before and after the collision.

A machine returns the ball to the person.

The machine takes 25.0 s to return the ball to the person.

The useful power output of the machine is 660 W.

Calculate the work done by the machine in returning the ball to the person.

Use the equation:

work done = power × time

The machine has an efficiency of 0.60

The useful power output of the machine is 660 W.

Calculate the total power input to the machine.

Use the equation:

The machine has several moving parts.

What is the name of the force caused by the moving parts rubbing together?

What happens to the wasted energy from the machine?

Tick (✓) one box.

The wasted energy cools the surroundings.

The wasted energy heats the surroundings.

The wasted energy is destroyed.

Figure 11 shows a steam engine pulling a train.

One type of steam engine burns coal as the fuel source.

The energy from the coal is used to accelerate a train.

Describe how the energy stores of the coal and the train change as the train accelerates.

Which equation links energy (E), power (P) and time (t)?

Tick (✓) one box.

A steam engine has a power output of 8000 W.

Calculate the energy output of the steam engine in 3600 seconds.

In the 18th century the power output of steam engines was measured in a unit called ‘horsepower’.

Suggest why the unit of horsepower was used.

Figure 1 shows a steam engine pulling a train.

One type of steam engine burns coal as the fuel source.

The energy from the coal is used to accelerate a train.

Describe how the energy stores of the coal and the train change as the train accelerates.

Which equation links energy (E), power (P) and time (t)?

Tick (✓) one box.

A steam engine has a power output of 8000 W.

Calculate the energy output of the steam engine in 3600 seconds.

In the 18th century the power output of steam engines was measured in a unit called ‘horsepower’.

Suggest why the unit of horsepower was used.

A student investigated how the power output of a filament lamp varied with the current in the lamp.

Figure 15 shows part of the circuit the student used.

To calculate power output the student measured the current in the lamp and the potential difference across the lamp.

Complete Figure 15 by adding an ammeter and a voltmeter to make the measurements.

Use the correct circuit symbols.

Which energy store in the battery decreases when the lamp is switched on?

What happens to the energy transferred by the lamp?

Figure 16 shows the results.

Describe how varying the current affects the power output of the filament lamp.

Write down the equation which links current (I), power (P) and resistance (R).

Determine the resistance of the lamp when the current in the lamp is 0.22 A

A student investigated how the bounce height of a ball varied with drop height.

Figure 4 shows the ball before and after bouncing.

Figure 5 shows some of the student’s results.

Describe a method the student could use to obtain the data shown in Figure 5.

Draw a ring around the anomalous result on Figure 5.

Give one reason why you chose this result.

Table 2 shows some of the student’s results.

Plot the data in Table 2 on Figure 5.

Draw a line of best fit.

What conclusion can be made from Figure 5 ?

Tick (✓) one box.

Table 3 shows some of the student’s results.

What was the uncertainty in the student’s results when the drop height was 60 cm?

Tick (✓) one box.

What is the reason for the uncertainty in the values of bounce height?

Tick (✓) one box.

A student investigated how the distance travelled by a trolley from the end of a ramp varied with the total mass of the trolley.

Figure 6 shows the equipment the student used.

This is the method used.

1. Put the trolley on the ramp at the start position.

2. Let the trolley roll down the ramp.

3. Measure the distance from the end of the ramp to the position where the trolley stops.

4. Repeat steps 1 to 3 with different masses on the trolley.

Give one variable the student should have kept the same in the investigation.

Table 4 shows the results.

Predict a value for X in Table 4.

What conclusion can be made from these results?

When the trolley was in the start position, the vertical height between the centre of mass of the trolley and the floor was 0.600 m

gravitational field strength = 9.8 N/kg

Calculate the gravitational potential energy of the trolley when the total mass of the trolley and masses was 2.50 kg

Use the equation:

gravitational potential energy = mass × gravitational field strength × height

When the trolley is released from the start position, energy is transferred in different ways.

Complete the sentences.

Choose answers from the box.

As the trolley moves down the ramp the trolley accelerates.

There is an increase in the trolley’s
energy.

After leaving the ramp the trolley slows down.

There is an increase in the
energy of

the surroundings.