Big question: if two people do the same work, why is one more powerful?
Make a prediction
Two trainees carry the same 10 kg bag up the same stairs. Asha takes 8 s. Baraka takes 16 s.
Who does more work on the bag?
Climb, time and measure
Press Climb. Read the height on the tape and the time on the stopwatch.
Mass lifted
Height h
Stopwatch
Energy gained by the load so far
Recorded readings
0 readings
Leave W and P empty. Work them out on your results sheet.
Work and power
Work done W = m × g × h. Power P = W ÷ t.
Worked solution (7 steps)
Check yourself
You climb the same stairs with the same bag, but twice as fast. What happens?
Calculate the power
Read the set-up, work out the power, then type your answer. Three rounds.
Score: 0 / 3
Big question: where does the electrical energy go when a kettle boils water?
Make a prediction
The same 2000 W kettle heats water from 25 °C to 80 °C. First 1 kg of water, then 2 kg.
How long does the 2 kg take, compared with the 1 kg?
Heat and time
Switch on. The kettle switches off by itself at the set temperature.
Thermometer
Stopwatch
Power label
Where the energy goes
To the water 0 kJLost to the air 0 kJEnergy in 0 kJ
Recorded readings
0 readings
| No. | P W | m kg | T₁ °C | T₂ °C | t s | E J | Q J | η % |
|---|
Leave E, Q and η empty. Work them out: E = P × t, Q = m c ΔT (c = 4200 J/(kg °C)), η = Q ÷ E × 100%.
Energy in, energy out
Energy in E = P × t. Energy to the water Q = m × c × ΔT. Efficiency η = Q ÷ E × 100%.
Worked solution (7 steps)
Check yourself
Why is the efficiency of a real kettle less than 100%?
Predict the heating time
Work out the time, type it, then switch on to test it. Three rounds.
Score: 0 / 3