Work and Energy — Questions

Calculate the work done when a force of 250 N moves an object 8 m in the direction of the force.

A crane lifts a 500 kg load a height of 12 m. Calculate the work done against gravity. (g = 9.8 N/kg)

A force of 60 N pushes a box 3.5 m across a floor at constant speed. Calculate the work done by the applied force.

A weightlifter lifts a 120 kg barbell from the floor to a height of 2 m. Calculate the work done against gravity. (g = 9.8 N/kg)

A shopping trolley is pushed with a force of 45 N over a distance of 12 m. Calculate the work done, then give your answer in kJ as well as J.

A machine does 3600 J of work moving a load 9 m. Calculate the force involved.

Calculate the kinetic energy of a 0.6 kg ball moving at 15 m/s.

A 1200 kg car increases its speed from 10 m/s to 25 m/s. Calculate the increase in its kinetic energy.

A crate of mass 8 kg is lifted 4 m onto a shelf. Calculate its gain in gravitational potential energy. (g = 9.8 N/kg)

A cyclist and bicycle have a combined mass of 75 kg and travel at 8 m/s. Calculate their kinetic energy.

A 1000 kg car has a kinetic energy of 125000 J. Calculate its speed.

A 60 kg hiker climbs a hill, gaining 850 m in height. Calculate the increase in her gravitational potential energy. (g = 9.8 N/kg)

A ball of mass 900 g is thrown at 20 m/s. Calculate its kinetic energy in joules.

A 5 kg object gains 245 J of gravitational potential energy after being raised. Calculate the height it was raised through. (g = 9.8 N/kg)

A ball of mass 0.2 kg is dropped from a height of 10 m. Ignoring air resistance, calculate its speed just before it hits the ground. (g = 9.8 N/kg)

A ball of mass 0.5 kg is thrown straight upward with a speed of 12 m/s. Ignoring air resistance, use conservation of energy to calculate the maximum height it reaches. (g = 9.8 N/kg)

A skier starts from rest at the top of a frictionless slope 25 m high. Calculate her speed at the bottom. (g = 9.8 N/kg, ignore air resistance)

A pendulum bob of mass 0.3 kg swings from a point 0.2 m above its lowest point. Ignoring air resistance, calculate its speed at the lowest point. (g = 9.8 N/kg)

A 400 kg roller-coaster car starts from rest at the top of a 20 m high hill. At the bottom, its speed is measured as 18 m/s.

Calculate the energy lost to friction and air resistance during the descent. (g = 9.8 N/kg)

A ball is thrown straight upward, reaches its highest point, and falls back down into the thrower’s hand. Ignoring air resistance, describe the energy transfers taking place throughout this motion.

A 0.4 kg ball is dropped from a height of 5 m onto a hard floor. It rebounds to a height of 3.2 m.

Calculate the percentage of its gravitational potential energy that is “lost” during the bounce (i.e. not returned as height on the rebound). (g = 9.8 N/kg)

A motor does 4500 J of work in 15 s. Calculate its power output.

A pump has a power rating of 2 kW and runs for 3 minutes. Calculate the total energy transferred, in joules.

A machine is supplied with 800 J of energy and produces 600 J of useful output. Calculate its efficiency.

A weightlifter raises a 100 kg barbell 2 m in 0.8 s. Calculate the useful power output. (g = 9.8 N/kg)

An electric motor has a power input of 500 W and a useful power output of 350 W. Calculate its efficiency.

A light bulb transfers 100 J of electrical energy, of which 20 J is usefully transferred as light and the rest as heat.

Calculate its efficiency, and state where the “lost” energy goes.

A pump has a power rating of 750 W. Calculate how long it takes to transfer 45000 J of energy.

A 3 kW heater runs for 2.5 hours.

Calculate the energy transferred in kWh, and the total cost if electricity costs $0.18 per kWh.

A 1500 kg car accelerates from rest to 20 m/s in 8 s.

Assuming all the work done by the engine goes into kinetic energy (ignore friction and air resistance), calculate the average power developed by the engine.