Question

How long will it take to stop a car travelling at a speed of 60 m/s, if the uniform acceleration during braking is – 12 m/s

Answer 1

Given:

Initial velocity of car,u= 60 m/s

Final velocity of car,v= 0 m/s

(Since, car stops finally)

Acceleration of car,a= -12 m/s²

To Find:

Time taken by car to stop

Solution:

We know that,

• According to first equation of motion for constant acceleration,

$\purple{\boxed{\bf{v=u+at}}}$

where,

v is final velocity

u is initial velocity

a is acceleration

t is time taken

$\rule{190}{1}$

Let the time taken by car to stop be t

So, on applying first equation of motion on car, we get

$\longrightarrow\rm{v=u+at}$

$\longrightarrow\rm{0=60+(-12)t}$

$\longrightarrow\rm{-60=-12t}$

$\longrightarrow\rm{-12t=-60}$

$\longrightarrow\rm{t=\dfrac{\cancel{-60}}{\cancel{-12}}}$

$\longrightarrow\rm\green{t=5\ s}$

Hence, the car will take 5 seconds to stop after applying brakes.

Answer 2

Given that ,

" A car travelling at a speed of 60 m/s, if the uniform acceleration during braking is  12 m/s² . We need to find how long will it take to stop the car "

Initial velocity , u = 60 m/s

Acceleration , a = - 12 m/s²

Finally car will stops .

So , Final velocity , v = o m/s

Time , t = ? s

Use 1st equation of motion to find time taken to stop the car .

⇒ v = u + at

⇒ 0 = 60 - 12t

⇒ 12t = 60

⇒ t = 5 seconds

So , car will take 5 seconds to stop after applying brakes