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JAMB Physics 2017 Paper

Question : 11

Total: 49

Solution:

Concept:

Efficiency of a machine is the ratio of mechanical advantage to velocity ratio, expressed as a percentage.

Explanation:

For a block and tackle with 6 pulleys, the velocity ratio equals the number of pulleys.

So,

V.R = 6

Mechanical advantage is given by:

M.A = \frac{\text{Load}}{\text{Effort}} = \frac{200}{50} = 4

Now calculate efficiency:

\text{Efficiency} = \frac{M.A}{V.R} \times 100\% = \frac{4}{6} \times 100\%

\text{Efficiency} = 66.67\%

Answer:

C. 66.7%

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