What type of energy is stored in a stretched elastic band?
Elastic potential energy.
A 400 W kettle runs for 3 minutes. How much energy does it transfer?
E = P × t = 400 × (3 × 60) = 72,000 J.
Define energy.
Energy is the ability to do work or cause change.
Write the equation linking work done, force, and distance.
W = F × s.
A car engine transfers 80,000 J of energy in 5 seconds. What is its power output?
P = E / t = 80,000 / 5 = 16,000 W (16 kW).
State the unit of energy.
Joule (J).
Name two ways to reduce unwanted energy transfers in a house.
Insulation (e.g. cavity wall or loft insulation), double glazing or draught proofing.
Write the equation for gravitational potential energy.
Ep = mgh.
A 1.8 kg ball is lifted 2.5 m. Calculate its increase in gravitational potential
energy (g = 9.8 m/s²).
Ep = 1.8 × 9.8 × 2.5 = 44.1 J.
Write the equation for kinetic energy.
Ek = ½ mv².
A person pushes a box with a force of 55 N over a distance of 2.5 m. Calculate the work done.
W = 55 × 2.5 = 137.5 J.
State the principle of conservation of energy.
Energy cannot be created or destroyed, only transferred or stored in different forms.
Calculate the kinetic energy of a 5 kg object moving at 4 m/s.
Ek = ½ × 5 × 4² = 40 J.
A light bulb transfers 150 J of energy every second but only 30 J as useful light. Calculate its efficiency.
Efficiency = (Useful output/total input) x 100 = (30 / 150) x 100 = 20%.
What is meant by a “closed system”?
A system where no energy is lost or gained from the surroundings.
