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WAEC Physics 2011 Paper

Question : 10

Total: 49

Solution:

Concept:

For a uniform metre rule balanced on a fulcrum, the clockwise moment equals the anticlockwise moment.

Explanation:

The mass of

120\text{ g}

is at the

10\text{ cm}

mark.

The fulcrum is at the

35\text{ cm}

mark.

Distance from the mass to the fulcrum is

35 - 10 = 25\text{ cm}

Since the rule is uniform, its centre of mass is at the

50\text{ cm}

mark.

Distance from the centre of the rule to the fulcrum is

50 - 35 = 15\text{ cm}

Let the mass of the rule be

M

For balance:

120 \times 25 = M \times 15

M = \frac{120 \times 25}{15} = 200\text{ g}

Answer:

200\text{ g}

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