IB Physics SL A 3 12 Power Questions

Practise calculating power from energy, work, force, speed and time across renewable, thermal and transport systems in exam questions.

Exam points

Calculate power as the rate of work or energy transfer, P = ΔW/Δt.
Relate power to force and velocity using P = Fv and interpret energy, work, time or velocity data with complete evidence.

[Maximum number: 2]

A 300 W immersion heater is placed in a beaker containing 0.25 kg of water at a temperature of $18^{\circ} \mathrm{C}$ . The heater is switched on for 120 s , after which time the temperature of the water is $45^{\circ} \mathrm{C}$ . The thermal capacity of the beaker is negligible and the specific heat capacity of water is $4.2 \times 10^{3} \mathrm{Jkg}^{-1} \mathrm{~K}^{-1}$ .

Determine the rate at which thermal energy is transferred from the water to the surroundings during the time that the heater is switched on.

energy transfer $=[300 \times 120]-\left[2.835 \times 10^{4}\right]=7.65 \times 10^{3} \mathrm{~J}$ ;
rate of transfer $=\frac{7.650 \times 10^{3}}{120}=64 \mathrm{~W}$ ;

Marking guidance:

Allow ECF from (b)(i).

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IB Physics SL A 3 12 Power Questions question 1