Question

please help me by telling me the answer

Answer 1

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Answer 2

72 kmph = 72×5/18 = 20 m/s

Final Velocity = 0 m/s

Distance covered = 100 metres

To find Retardation we'll use the 3 equation of uniformly accelerated motion.

${v}^{2} = {u}^{2} + 2as \\ {0}^{2} = {20}^{2} + 2 \times a \times 100 \\ - 400 = 200a \\ 200a = - 400 \\ a = \frac{ - 400}{200} \\ a = - 2 \: m {s}^{ - 2}$
Retardation = 2 m/s²

To find time taken We can use 1st equation of uniformly accelerated motion.

$v = u + at \\ 0 = 20 + ( - 2 \times t) \\ - 20 = - 2t \\ 2t = 20 \\ t = 10 \: seconds.$
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