Work, energy and efficiency explorer
Track a trolley’s gravitational, kinetic and thermal energy, vary friction and compare energy transfer in two motors lifting the same load.
Learning goals
- Recognise kinetic, potential, nuclear and internal energy stores
- Describe mechanical energy transfer by a force acting over a distance
- Describe electrical energy transfer by an electric current
- Describe energy transfer by heating due to a temperature difference
- Describe energy transfer by electromagnetic and mechanical waves
- Recall and apply Ek = ½mv² in new situations
- Recall and apply Ep = mgh near the Earth's surface in new situations
- State and apply the principle of conservation of energy
- Recall and apply work done = force × distance moved in the force direction
- Recall and apply power = energy transfer / time taken
- Calculate efficiency as useful energy output / total energy input
A 2 kg trolley released from 3.0 metres with no friction. It is 3.00 metres up at 0.00 metres per second. GPE 58.9 J, KE 0.0 J, thermal 0.0 J.
- Height, h
- 3.00 m
- Speed, v
- 0.00 m s−1
- Kinetic energy
- 0.0 J
- Gravitational potential energy
- 58.9 J
- Internal energy of the surroundings
- 0.0 J
- Energy supplied
- 0 J
- GPE gained (useful)
- 0 J
- Wasted energy
- 0 J
- Efficiency
- — %
Try this
0 of 4 doneWith no friction, release the trolley from 3.0 m and find its speed at the bottom. (not done yet)
All the GPE becomes KE at the bottom: mgh = ½mv², so v = √(2gh) ≈ 7.7 m/s whatever the mass.
With no friction, record the speed at the bottom for five release heights. (not done yet)
v² is proportional to h: the gradient of the v²–h graph is 2g.
Add friction and let the trolley come to rest. (not done yet)
The trolley's kinetic energy is zero. Some initial gravitational potential energy may remain if static friction holds it above the lowest point; the rest has increased internal energy in the trolley, track and air. The total energy has not changed.
Lift the same crate with the new motor and the old motor at the same power. (not done yet)
Both give the crate the same GPE, but the less efficient motor needs more energy supplied, and the extra is dissipated to the internal store of the surroundings. It also takes longer.
You’ve tried every task.
Your readings
| # | h / m | v / m s−1 | v2 / m2 s−2 | Remove |
|---|---|---|---|---|
| No readings yet. Set up a measurement, then record it. | ||||