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WAEC Physics 2011 Paper

Question : 15

Total: 49

The radius of a wheel is 30.0 cm and that of its axle is 6.0cm. Calculate the effort required to lift a load of 120.0N using this machine. Assuming 100% efficiency

600.0N
40.0N
24.0N
20.0N

Validate

Solution:

Concept:

For a wheel and axle, the velocity ratio is the ratio of the wheel radius to the axle radius. At 100% efficiency, mechanical advantage equals velocity ratio.

Explanation:

Radius of wheel,

R = 30.0\ \text{cm}

Radius of axle,

r = 6.0\ \text{cm}

Velocity ratio,

V.R = \frac{R}{r} = \frac{30.0}{6.0} = 5

Since efficiency is 100%,

Mechanical advantage,

M.A = V.R = 5

Using the machine relation:

M.A = \frac{\text{Load}}{\text{Effort}}

\text{Effort} = \frac{\text{Load}}{M.A} = \frac{120.0\ \text{N}}{5}

\text{Effort} = 24.0\ \text{N}

Answer:

The effort required is

24.0\ \text{N}

. Correct option: C.

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