Question

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Answer 1

${\huge{\underline{\underline{\mathrm{\red{GiveN::}}}}}}$
m = 100 kg
u ( initial velocity ) = 60km/h = 60×18/5m/s = 216m/s
t = 5s
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As , The car stops within 5s so the final velocity will be zero.
::$\tt\implies$ v ( final velocity ) = 0

${\huge{\underline{\underline{\mathrm{\pink{AnsweR::}}}}}}$
F = mass × acceleration = m×a
As , acceleration = (v-u)/t
$\tt\implies$ a = (0-216)/5
$\tt\implies$ a = -216/5
$\tt\implies$ a = -43.2m/s²

Here , the acceleration is negative as the velocity is decreasing which defines that there is a retardation.
So , retardation = 43.2 m/s²
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NOTE :- While writing the negative acceleration in terms of retardation , the negative sign is not considered.
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${\huge{\underline{\underline{\mathrm{\orange{ThereforE::}}}}}}$
F = m×a
F = (100×43.2) N
F = 4320.0 N
F = 4320 Newton (N).