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WAEC Physics 2011 Paper

Question : 3

Total: 49

Solution:

Concept:

Density relates mass to the volume of the rod.

Volume is the product of cross-sectional area and length.

Explanation:

Density is given by

\rho = \frac{m}{V}

For the rod,

V = A L

, where

A

is cross-sectional area and

L

is length.

Rearrange the formula to get

L = \frac{m}{\rho A}

Substitute the given values:

m = 1.76\, \text{kg}

\rho = 7000\, \text{kg m}^{-3}

, and

A = 0.001257\, \text{m}^2

Calculate:

L = \frac{1.76}{7000 \times 0.001257}

This gives

L = 0.2\, \text{m}

Answer:

0.20\, \text{m}

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