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JAMB Physics 2010 Paper

Question : 37

Total: 47

Solution:

Concept:

The work done by the gradually applied horizontal force is equal to the gain in gravitational potential energy of the bob.

Explanation:

Weight of bob,

W = 0.1\,\mathrm{N}

Length of string,

L = 50\,\mathrm{cm} = 0.5\,\mathrm{m}

When the string makes

60^\circ

with the vertical, the bob rises by

h = L - L\cos 60^\circ = L(1 - \cos 60^\circ)

Since

\cos 60^\circ = \frac{1}{2}

h = 0.5\left(1 - \frac{1}{2}\right) = 0.5 \times \frac{1}{2} = 0.25\,\mathrm{m}

The bob starts and ends at rest, so the work done equals the increase in potential energy.

Work done

= Wh = 0.1 \times 0.25 = 0.025\,\mathrm{J}

Answer:

0.025\,\mathrm{J}

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