Question

If a bus travelling at 20 m/sec is subject to a steady deceleration of 5 m/sec2, how long will it take to come to rest?

Answer 1

$\small{\underline{\sf{\orange{Given:\rightarrow}}}}$

Initial Velocity, u = 20 m/s

Final Velocity, v = 0 m/s

Acceleration, a = -5m/s²  (minus due to deceleration)

$\small{\underline{\sf{\green{Find:\rightarrow}}}}$

Time-?

$\small{\underline{\sf{\red{Formula \ used :\rightarrow}}}}$

$\boxed{\sf{a= \dfrac{v-u}{t}}}$

$\small{\underline{\sf{\blue{SoLution:\rightarrow}}}}$

Putting values in formula we get,

$\sf{\implies -5=\dfrac{0-20}{t}}$

$\sf{\implies t= \dfrac{-20}{-5}}$

$\sf{\implies t= 4 \ sec}$

hence, Bus will take 4 sec to come to rest .

_____________________________

Answer 2

Given ,

Initial velocity (u) = 20 m/s

Final velocity (v) = 0 m/s

Acceleration (a) = - 5 m/s² (deceleration)

We know that , the Newton's first equation of motion is given by

$\boxed{ \sf{v = u + at}}$

Thus ,

0 = 20 + (-5)t

-20 = -5t

t = -20/-5

t = 4 sec

$\therefore$ A bus will take 4 sec to come to rest