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WAEC Physics 2017 Paper

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Question : 11

Total: 50

A motorist travelling at 72

\text{kmh}^{-1}

had his eyes shut for 0.4s during a hard sneeze. Calculate the distance covered by him during this time interval.

50.0m
28.8m
18.0m
8.0m

Solution:

Concept:

When speed is constant, distance covered equals speed multiplied by time.

Explanation:

First, convert the speed from

\mathrm{kmh}^{-1}

to

\mathrm{ms}^{-1}

.

Since

1\ \mathrm{km} = 1000\ \mathrm{m}

and

1\ \mathrm{h} = 3600\ \mathrm{s}

,

72\ \mathrm{kmh}^{-1} = 72 \times \frac{1000}{3600}\ \mathrm{ms}^{-1} = 20\ \mathrm{ms}^{-1}

.

The time during which the eyes were shut is

0.4\ \mathrm{s}

.

Distance covered is given by:

d = 20\ \mathrm{ms}^{-1} \times 0.4\ \mathrm{s} = 8\ \mathrm{m}

.

Answer:

D.

8.0\ \mathrm{m}

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