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WAEC Physics 2014 Paper

Question : 23

Total: 48

^{-1}

Solution:

Concept:

Power is the rate at which work is done. For a constant force opposing motion, power is the product of force and velocity.

Explanation:

The engine must produce power to overcome the frictional resistance.

Power,

P = F \times v

Here,

F = 100\ \mathrm{N}

and

v = 30\ \mathrm{m\,s^{-1}}

So,

P = 100 \times 30 = 3000\ \mathrm{W} = 3\ \mathrm{kW}

Given

1\ \mathrm{hp} = 0.75\ \mathrm{kW}

, convert the power to horsepower:

P = \frac{3}{0.75} = 4\ \mathrm{hp}

Answer:

The power developed by the engine is

4.00\ \mathrm{hp}

Correct option: C. 4.00hp.

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