GCSE / IGCSE Physics – Energy
Energy stores, efficiency, work and power, specific heat capacity.
This worksheet covers:
- This worksheet covers energy stores
- Work
- Power
- Efficiency
- Specific heat capacity
A calculator is allowed throughout; take $g=9.8\,\text{N/kg}$ unless stated otherwise, and use $c_{\text{water}}=4200\,\text{J/kg}^{\circ}\text{C}$.
Questions
A crane lifts a $250\,\text{kg}$ load through a vertical height of $12\,\text{m}$. Calculate the work done against gravity.
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A force of $60\,\text{N}$ pushes a box a distance of $8\,\text{m}$ across a floor. Calculate the work done by the force.
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Define “power” and state its unit.
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An electric motor transfers $4500\,\text{J}$ of energy in $15\,\text{s}$. Calculate its power output.
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An electric kettle has a power input of $2000\,\text{W}$. In one minute of use, $96\,000\,\text{J}$ of energy is usefully transferred to heat the water, and the rest is wasted as heat to the surroundings.(a) Calculate the total energy input to the kettle in one minute.(b) Calculate the efficiency of the kettle, giving your answer as a percentage.
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$0.5\,\text{kg}$ of water is heated from $20^{\circ}\text{C}$ to $80^{\circ}\text{C}$ using an immersion heater.(a) Calculate the energy required to heat the water.(b) The heater has a power rating of $1000\,\text{W}$ and is 100% efficient. Calculate how long it takes to heat the water.
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Explain, in terms of energy stores and transfers, what happens to the kinetic energy of a car as its brakes are applied and it comes to rest.
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A ball of mass $0.2\,\text{kg}$ is dropped from a height of $5\,\text{m}$. Calculate its speed just before hitting the ground, assuming all the gravitational potential energy is transferred to kinetic energy and air resistance is negligible.
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A hydroelectric power station has a reservoir $40\,\text{m}$ above its turbines. Water flows through the turbines at a rate of $50\,000\,\text{kg}$ per second.(a) Calculate the maximum power that could be generated, assuming 100% efficiency.(b) The station actually generates $15\,\text{MW}$ of electrical power. Calculate its efficiency.
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A cyclist and bike have a total mass of $80\,\text{kg}$. The cyclist accelerates from rest to $6\,\text{m s}^{-1}$.(a) Calculate the kinetic energy gained.(b) If the cyclist’s legs do $1800\,\text{J}$ of work to reach this speed, calculate the efficiency of energy transfer to kinetic energy.
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A $2\,\text{kW}$ immersion heater raises the temperature of $10\,\text{kg}$ of water by $15^{\circ}\text{C}$, with no energy losses. Calculate the time taken, giving your answer in minutes.
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A pendulum bob of mass $0.3\,\text{kg}$ swings from a height of $0.2\,\text{m}$ above its lowest point. Assuming no air resistance, calculate its maximum speed at the lowest point.
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