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Driver of a c...

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Driver of a car moving at $72 k m / h$ spot a kid $100$ m head.if the reaction time is $1$ sec. Then minimum retardation,he will apply to save the kid is:

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Solution

$u = 72 k m p h = 72 \times \frac{5}{18} = 20 m / s$
distance travelled in $1 s e c = 20 \times 1 = 20 m$
remaining distance $= 100 - 20 = 80 m$
$V^{2} - u^{2} = 2 a s$
$\Rightarrow 0 - 400 = - 2 a (80)$
$= a = \frac{400}{160} = \frac{10}{4} = 2.5 m / s^{2}$

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