1.7.4 Power (3)
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1.
A student lifts a 5kg weight vertically by 1m in 2 seconds. Calculate the power output of the student. Show your working.
Given:
- Mass (m) = 5 kg
- Height (h) = 1 m
- Time (t) = 2 s
Calculate the potential energy gained by the weight:
Potential Energy (PE) = mgh = 5 kg * 9.8 m/s² * 1 m = 49 J
Calculate the work done by the student:
Work done (W) = Force (F) * Distance (d)
The force required to lift the weight is equal to the weight of the object: F = mg = 5 kg * 9.8 m/s² = 49 N
Work done (W) = 49 N * 1 m = 49 J
Calculate the power output of the student:
Power (P) = Work done (W) / Time (t) = 49 J / 2 s = 24.5 W
Answer: The power output of the student is 24.5 W.
2.
Define power in terms of work done and time, and in terms of energy transferred and time. State the relevant equations.
Definition: Power is the rate at which work is done, or the rate at which energy is transferred.
Work done per unit time: Power (P) = Work done (W) / Time (t) or P = W / t
Energy transferred per unit time: Power (P) = Energy transferred (ΔE) / Time (t) or P = ΔE / t
3.
A motor transfers 120 J of energy in 5 seconds. Calculate the power of the motor. State the equation you used.
Equation used: P = ΔE / t
Given:
- Energy transferred (ΔE) = 120 J
- Time (t) = 5 s
Calculate the power of the motor:
Power (P) = ΔE / t = 120 J / 5 s = 24 W
Answer: The power of the motor is 24 W.