Edexcel A-Level Physics Power, Time and Energy Transfer

Practise Edexcel A-Level Physics power, time and energy transfer through P=E/t, P=Fv, work-rate calculations, kWh conversion and energy comparison claims.

Exam points

use P=E/t, W/t or P=Fv to calculate power, force, time or transferred energy
convert or compare joules, watts and kilowatt-hours in energy-transfer contexts
assess claims by comparing power-time energy transfers from motors, water or heaters

[Maximum number: 2]

The diagram shows a system used to move a stone block up a ramp. A team of people uses a rope to pull the block at a constant speed.

Figure for Question 1.3.21 - Power, time and energy transfer question 1 — Edexcel A-Level Physics AS

height of ramp $=4.35 \mathrm{~m}$
angle of ramp to horizontal $=6.0^{\circ}$
mass of block $=2.10 \times 10^{3} \mathrm{~kg}$
speed of block up ramp $=0.450 \mathrm{~m} \mathrm{~s}^{-1}$
total power of team $=6.25 \mathrm{~kW}$

Show that the total force that the team exerts on the block is about 14 kN .
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Use of P=W / t and $\Delta W=F \Delta s$

Force = 13.9(kN)

Example of calculation

In 1 second $W=6250 \mathrm{~J}$ and distance travelled $=0.450 \mathrm{~m}$ $F=6250 \mathrm{~W} \div 0.450 \mathrm{~m} \mathrm{~s}^{-1}=13.9 \mathrm{kN}$

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1.3.21 - Power, time and energy transfer question 1