Ncert Exercises & Solutions

A car moving along a straight highway with speed of 126 km h^–1 is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop?
1. $1.5~\text{m/s}^2,~20~\text s$
2. $2.5~\text{m/s}^2,~15~\text s$
3. $3.06~\text{m/s}^2,~11.4~\text s$
4. $4.2~\text{m/s}^2,~8.5~\text s$

:Initial velocity of the car, u = 126 km/h = 35 m/s

Final velocity of the car, v = 0

Distance covered by the car before coming to rest, s = 200 m

Retardation produced in the car = a

$W e k n o w t h a t,$
$v^{2} - u^{2} = 2 a s$
$(0) - {(35)}^{2} = 2 \times a \times 200$
$a = - \frac{35 \times 35}{2 \times 200} = - 3.06 m / s^{2}$
$U \sin g,$
$v = u + a t$
$t = \frac{v - u}{a} = \frac{0 - 35}{(- 3.06)} = 11.44 s$

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