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WAEC Physics 2011 Paper

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Question : 20

Total: 49

A body is pulled over a distance of 500m by a force of 20N. If the power developed is o.4 kW, calculate the time interval during which the force is applied

0.2s
2.5s
25.0s
250.0s

Solution:

Concept:

Power is the rate of doing work, so time is work done divided by power.

Explanation:

Work done by the force is

W = F \times s = 20 \times 500 = 10000\ \mathrm{J}

.

Convert power to watts:

P = 0.4\ \mathrm{kW} = 0.4 \times 1000 = 400\ \mathrm{W}

.

Time interval is

t = \dfrac{W}{P} = \dfrac{10000}{400} = 25\ \mathrm{s}

.

Therefore, the correct time is

25.0\ \mathrm{s}

.

Answer:

C.

25.0\ \mathrm{s}

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