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WAEC Physics 2011 Paper

Question : 9

Total: 49

Solution:

Concept:

The kinetic energy gained equals the loss in gravitational potential energy as the stone falls.

Explanation:

Mass of stone:

300\text{ g} = 0.3\text{ kg}

The stone falls a quarter of the building height:

\frac{100}{4} = 25\text{ m}

Height remaining above the ground:

100 - 25 = 75\text{ m}

Kinetic energy gained

= mg(h_{\text{initial}} - h_{\text{final}})

Substitute values:

= 0.3 \times 10 \times (100 - 75)

Simplify:

= 0.3 \times 10 \times 25 = 75\text{ J}

Answer:

75.0\text{ J}

(Option C).

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