Sec 3 Physics Energy, Work & Power topical questions

Name the main energy store, and the pathway, in each case.

1. (a)A stretched catapult band about to launch a pebble.[1]
2. (b)The pebble flying through the air.[1]
3. (c)A cup of tea cooling on a desk.[1]
4. (d)Sunlight warming a black water pipe.[1]

A 3.0 kg bowling ball rolls at 2.0 m/s.

1. (a)Calculate its kinetic energy.[2]
2. (b)The ball’s speed doubles. State its new kinetic energy.[1]

A weightlifter raises a 60 kg barbell 2.0 m at constant speed. Take g = 10 N/kg.

1. (a)Calculate the weight of the barbell.[1]
2. (b)Calculate the work done lifting it.[2]
3. (c)State the gravitational potential energy gained.[1]

A rollercoaster car of mass 400 kg is hauled to the top of a 25 m first hill and then released. Friction is negligible. Take g = 10 m/s².

1. (a)Calculate the gravitational potential energy at the top.[2]
2. (b)Calculate the maximum kinetic energy of the car during the ride.[1]
3. (c)Calculate the car’s speed at the bottom of the first drop.[2]
4. (d)The second hill is 15 m high. Explain whether the car can reach its top.[1]

A warehouse worker pushes 8 crates of 12 kg each up a 3.0 m ramp to a loading bay. The ramp is 6.0 m long. Take g = 10 N/kg.

1. (a)Calculate the total weight moved.[1]
2. (b)Calculate the useful work done against gravity.[2]
3. (c)Explain why the answer uses 3.0 m and not 6.0 m.[2]
4. (d)The worker actually transfers 4.0 kJ. Calculate the efficiency of the operation.[1]

An electric kettle is rated 2.0 kW. It heats 1.5 kg of water from 20 °C to 100 °C in 4.5 minutes. (Specific heat capacity of water = 4200 J/(kg·°C).)

1. (a)Calculate the energy usefully delivered to the water.[2]
2. (b)Calculate the electrical energy supplied.[2]
3. (c)Calculate the kettle’s efficiency.[2]
4. (d)State the destination of the wasted energy.[1]

A pupil times herself running up a flight of steps of vertical height 2.8 m. Her mass is 45 kg and the climb takes 4.0 s. Take g = 10 N/kg.

1. (a)Calculate her useful power output.[3]
2. (b)A second pupil of the same mass takes 8.0 s. Compare his power with hers.[1]
3. (c)Explain why both pupils transfer more energy in total than the mgh value.[1]

A stone of mass 0.30 kg is fired vertically upwards at 15 m/s. Ignore air resistance. Take g = 10 m/s².

1. (a)Calculate the initial kinetic energy.[2]
2. (b)Calculate the maximum height gained.[3]
3. (c)Calculate the stone’s speed when it has risen 5.0 m.[2]

A pump lifts 2000 kg of water per minute through 15 m. Its motor draws 6.0 kW. Take g = 10 N/kg.

1. (a)Calculate the useful work per minute.[2]
2. (b)Calculate the useful power output and the efficiency.[4]
3. (c)The pump is connected to solar panels rated 8.0 kW at midday. Comment on whether the pump can run at full flow then, and in the morning.[2]

A ball of mass 0.20 kg is dropped from 2.5 m and rebounds to 1.8 m. Take g = 10 m/s².

1. (a)Calculate the energy before and after the bounce.[2]
2. (b)Calculate the energy transferred away from the ball’s mechanical stores at the bounce.[1]
3. (c)Calculate the speed just before impact.[2]
4. (d)A classmate says the missing energy was "destroyed in the thud". Assess.[2]

A village installs a 2.0 MW wind turbine. It generates at full power for 30% of the hours in a year (8760 h) and at zero for the rest.

1. (a)Calculate the energy generated in a year, in kW h.[3]
2. (b)A typical home uses 3600 kW h per year. Estimate how many homes the turbine supplies.[1]
3. (c)State the reliability problem this calculation reveals, and one system-level solution.[3]

A 65 kg athlete on an exercise bike pedals against a brake that absorbs 240 W of mechanical power for 30 minutes. Her body’s efficiency at delivering mechanical power is 22%. Take g = 10 N/kg.

1. (a)Calculate the mechanical energy delivered to the brake.[2]
2. (b)Calculate the total energy her body transfers.[2]
3. (c)Calculate the height of a hill she could climb with the same mechanical energy.[2]
4. (d)State the destination of the non-mechanical energy and one everyday observation that shows it.[2]