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WAEC Physics 2012 Paper

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Question : 17

Total: 47

A body is pulled through a distance of 500m by a force of 20N. If the power developed is 0.4kW, calculate the time for which the force acts

250.0s
25.0s
2.5s
0.5s

Solution:

Concept:

Work done by a constant force is equal to the product of power and time.

Explanation:

Work done is:

W = F \times d = 20 \times 500 = 10000 \, \text{J}

Power is given as:

0.4 \, \text{kW} = 400 \, \text{W}

Since power is work per unit time:

P = \frac{W}{t}

Therefore,

t = \frac{W}{P} = \frac{10000}{400} = 25.0 \, \text{s}

Answer:

25.0 \, \text{s}

, i.e. option B.

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