Energy, Work and Power

Describe the transfers between energy stores that occur as the load is lifted.

By comparing the input energy and the useful output energy, explain why the efficiency is less than 100%.

Explain how the principle of conservation of energy applies in lifting the load.

The input power to the motor is $15\ \text{W}$. The motor is used for $20\ \text{s}$. The efficiency of the motor is 60%.

Calculate the energy supplied to the load.

energy = ______ $\text{J}$

Define ‘power’.

The efficiency of the motor is 70%.

Calculate the input power to the motor.

input power = ______ $\text{W}$

Calculate the work done in lifting the load.

work done = ______ $\text{J}$

Calculate the time taken to lift the load.

time taken = ______ $\text{s}$

Describe how energy is transferred to thermal energy as the load is lifted by the fork-lift truck.

State the name of the energy store in the battery.

Describe, in terms of work done, the stages of energy transfer from the energy store in the battery to the kinetic energy of the scooter.

The total mass of the scooter and the rider is $70\text{ kg}$.

Calculate the total kinetic energy of the rider and scooter when the scooter has a speed of $4.0\text{ m / s}$.

kinetic energy = ______ $\text{J}$

Define what is meant by a kilowatt-hour.

The scooter stops working because the battery is totally discharged (flat). This means that there is no more energy stored in the battery.

The battery is then recharged using a $70\text{ W}$ power supply.

Calculate the time taken to fully recharge the battery.

time = ______ hours

The wind blows directly towards the turbine with a speed of $12\ \text{m / s}$.

In one second, $60\,000\ \text{kg}$ of air passes through the circular area swept out by the blades.

Calculate the kinetic energy of this mass of air.

kinetic energy = ______

State one reason why it is important to reduce the amount of carbon dioxide produced.

Suggest one advantage of using a coal-fired power station compared with a wind turbine.

Define the kilowatt-hour ($\text{kW\,h}$).

Calculate the mass of carbon dioxide saved when the wind turbine has a power output of $2000\ \text{kW}$ and operates for 12 hours.

mass = ______

Wind energy is a form of renewable energy.

State the name of one other form of renewable energy.

Calculate the change in gravitational potential energy (g.p.e.) of the car as it travels from A to B.

change in g.p.e. = ______

Calculate the speed of the car when it reaches B.

speed = ______

Explain, in terms of energy, why the car does not go past D, which is also $0.45\text{ m}$ above the horizontal track.

Immediately after being released at A, the car travels to B, to C and then to D.

Describe the motion of the car after it reaches D.

State the form of energy in the coal that is transferred to electrical energy.

State the principle of the conservation of energy.

The quantity of electrical energy produced by the power station is much less than the quantity of energy in the coal that is burnt to generate the electricity.

Explain why this is so.

State one environmental consequence of generating electricity in coal-fired power stations.

Calculate the gravitational potential energy gained by the wheelbarrow and its load.

$\text{energy} = \text{\_\_\_\_\_\_}$

The worker pushes the wheelbarrow $2.0\text{ m}$ along the plank.

Calculate the work done on the wheelbarrow by the worker.

$\text{work done} = \text{\_\_\_\_\_\_}$

Suggest one reason why the answer to (a)(ii) is not equal to the answer to (a)(i).

State what is meant by efficiency.

Suggest one reason why this method of lifting the load onto the platform is so inefficient.

Define what is meant by work done.

The mass of the flag is $0.35\ \text{kg}$ and the flag is raised through a height of $6.0\ \text{m}$.

The gravitational field strength $g$ is $10\ \text{N / kg}$.

Calculate the increase in gravitational potential energy of the flag.

gravitational potential energy = ______

Suggest and explain a reason why the work done on the rope is larger than the value calculated in (b).

Calculate the increase in gravitational potential energy of the load.

gravitational potential energy = ______

State the formula that relates efficiency, energy input and useful energy output.

Calculate the energy input to the motor.

energy input = ______

Suggest one reason why the efficiency of the motor is less than 1.0 (100%).

State the name of the form of energy stored in the oil before it is burnt.

State and explain whether oil is a renewable or a non-renewable energy source.

Describe one environmental issue caused by burning oil to generate electricity in a power station.

State what is meant by efficiency.

the input power to the power station,

input power = ______

the energy wasted in $2.0\text{ hours}$.

energy wasted = ______