IGCSE Physics Energy & power topical questions

Name the main energy store in each example.

1. (a)A bowl of breakfast cereal[1]
2. (b)A comet travelling through space[1]
3. (c)Water held behind a dam[1]

A torch uses a battery to light a bulb.

1. (a)Name the energy store that empties as the torch runs.[1]
2. (b)Name the store that fills in the surroundings as the bulb warms the air.[1]
3. (c)State the principle that requires the energy outputs to equal the input.[1]
4. (d)The battery delivered 2400 J and the light output was 300 J. State the energy transferred to heating.[1]

A crane does 4800 J of useful work lifting a steel beam through a height of 6.0 m.

1. (a)Write the equation linking work, force and distance.[1]
2. (b)Calculate the average lifting force.[2]
3. (c)State the unit of work.[1]

A warehouse worker pushes a trolley with a steady horizontal force of 60 N while it moves 15 m along a level aisle. Friction on the trolley is also 60 N.

1. (a)Work out the energy transferred by the push.[2]
2. (b)State the resultant horizontal force on the trolley.[1]
3. (c)Describe the trolley’s motion and explain your answer.[1]

A 1400 kg car travels at 25 m/s.

1. (a)Calculate the kinetic energy of the car.[2]
2. (b)The driver brakes and the speed falls to 12 m/s. Calculate the kinetic energy removed.[2]

A pumped-storage power station releases water from a reservoir 250 m above its turbines. Each second, 400 kg of water flows down.

1. (a)Calculate the gravitational potential energy released each second. Take g = 9.8 N/kg.[2]
2. (b)The station delivers 680 000 J of electrical energy each second. Calculate its efficiency.[2]
3. (c)State what happens to the rest of the energy.[1]

A student compares three resources for a new power station: natural gas, wind, and nuclear fission.

1. (a)State one advantage and one disadvantage of natural gas.[2]
2. (b)State one advantage and one disadvantage of wind.[2]
3. (c)Name the shared component (boiler, turbine, generator) that gas stations use but wind turbines do not need, and explain why.[2]

A 0.045 kg golf ball leaves the tee horizontally at 40 m/s. Air resistance is negligible for this question. Take g = 9.8 N/kg.

1. (a)Calculate the kinetic energy of the ball as it leaves the tee.[2]
2. (b)If all of this kinetic energy could transfer to gravitational potential energy, calculate the maximum height the ball could reach.[3]
3. (c)In reality the ball never rises this high. Give one reason.[1]

Machine X performs 1200 J of useful work in 30 s. Machine Y performs 1500 J of useful work in 50 s.

1. (a)Calculate the useful power of machine X.[2]
2. (b)Calculate the useful power of machine Y.[1]
3. (c)State which machine is the more powerful, and define power in your answer.[2]

A cyclist and bicycle of total mass 90 kg freewheel down a hill. They descend through a vertical height of 18 m, reaching a speed of 11 m/s at the bottom.

1. (a)Calculate the gravitational potential energy transferred during the descent. Take g = 9.8 N/kg.[2]
2. (b)Calculate the kinetic energy at the bottom.[2]
3. (c)Explain why the answers differ and state the missing energy’s destination.[2]

An electric motor is 65% efficient. It lifts a 25 kg load at a steady speed, raising it 9.0 m in 20 s. Take g = 9.8 N/kg.

1. (a)Calculate the useful work done lifting the load.[2]
2. (b)Calculate the useful power output of the motor.[2]
3. (c)Calculate the total electrical power supplied to the motor.[2]
4. (d)State where the wasted power goes.[1]

Each second, a power station receives 1000 MJ of chemical energy from coal and converts 40% of it into electrical energy. The electricity then drives motors at a factory, which are 80% efficient at converting electrical energy into useful mechanical work.

1. (a)Calculate the electrical energy delivered each second.[1]
2. (b)State the energy wasted by the power station each second and name its destination store.[1]
3. (c)Calculate the useful mechanical work delivered by the factory motors each second.[2]
4. (d)Calculate the overall efficiency of the chain from coal to mechanical work.[1]