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WAEC Physics 2015 Paper

Question : 17

Total: 50

Solution:

Concept:

The efficiency of a machine compares the mechanical advantage to the velocity ratio.

Explanation:

From the diagram, the velocity ratio is

VR = 6

Mechanical advantage is

MA = \frac{\text{Load}}{\text{Effort}} = \frac{100}{E}

Efficiency is given by:

\text{Efficiency} = \frac{MA}{VR} \times 100\%

Substitute the given values:

75 = \frac{\frac{100}{E}}{6} \times 100

75 = \frac{10000}{6E}

Multiply both sides by

6E

75 \times 6E = 10000

450E = 10000

E = \frac{10000}{450} = 22.2N

Answer:

The value of

E

22.2N

, which is Option A.

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