On turning a corner, a motorist rushing at 40 m / s, finds a child on the road 108 m ahead. He instantly stops the engine and applies the brakes so as to stop it within 1 m of the child, what time is required to stop it?

Question

On turning a corner, a motorist rushing at 40 m / s, finds a child on the road 108 m ahead. He instantly stops the engine and applies the brakes so as to stop it within 1 m of the child, what time is required to stop it? (A) 5.4 second (B) 6.4 second (C) 3.9 second (D) 2 second

Tardigrade Admin · Accepted Answer

2 as =v2-u2 a=(v2-u2/2 s)=(0-(40)2/2 × 108)=(-1600/216) a=-7.4 m / s 2 And. v = u + a v-u=a t ∴ t=(v-u/a)=(0-(40)/-7.4)=(-40/-7.4)=5.4 s

Q. On turning a corner, a motorist rushing at $40 m / s$ , finds a child on the road $108 m$ ahead. He instantly stops the engine and applies the brakes so as to stop it within $1 m$ of the child, what time is required to stop it?

5.4 second

6.4 second

3.9 second

2 second

2 as $= v^{2} - u^{2}$
$a = \frac{v ^{2} - u ^{2}}{2 s} = \frac{0 - ( 40 ) ^{2}}{2 \times 108} = \frac{- 1600}{216}$
$a = - 7.4 m / s^{2}$
And.
$v = u + a$
$v - u = a t$
$∴ t = \frac{v - u}{a} = \frac{0 - ( 40 )}{- 7.4} = \frac{- 40}{- 7.4} = 5.4 s$

Q. On turning a corner, a motorist rushing at 40m/s, finds a child on the road 108m ahead. He instantly stops the engine and applies the brakes so as to stop it within 1m of the child, what time is required to stop it?