When a car driver travelling at a speed of $10\ m/s$ applies brakes and brings the car to rest in $20\ s$, then retardation will be:
(a) $+2\ m/s^2$
(b) $-2\ m/s^2$
(c) $-0.5\ m/s^2$
(d) $+0.5\ m/s^2$

Academic Physics NCERT Class 9

Initial velocity $u=10\ m/s$

Final velocity $v=0$

Time $t=20\ s$

Therefore, retardation $a=\frac{v-u}{t}$

$=\frac{0-10}{20}$

$=\frac{-10}{20}$

$=-0.5\ m/s^2$

Therefore, option (b) is correct.

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Updated on: 10-Oct-2022

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