Question

A car is moving with a velocity of 72 km per hour . Its velocity is reduced to 36 km per hour after covering a distance of 200M. calculate retardation in centimetres per second square.

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Answer 1

$v = 72kmph = 72 \times \frac{5}{18} = 20 \: metre \: per \: seconds \\ u = 36kmph = 36 \times \frac{5}{18} = 10 \: metre \: per \: seconds \\ s = 200 \: m \\ v {}^{2} = u {}^{2} + 2as \\ 20 {}^{2} = 10 {}^{2} + 2 \times a \times 200 \\ 400 = 100 + 400a \\ 400a = 400 - 100 \\ 400a = 300 \\ a = \frac{300}{400} = \frac{3}{4} = 0.75$
$a = 0.75m \: per \: second {}^{2} \\ = \frac{75 \times 100}{100} \\ = 75$
So,retardation is 75cm/s^2.

Answer 2

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