Question

A car moving along a straight road with a speed of 144 kilometre per hour is brought to a stop within a distance of 200 m how long does it take for the car to stop?

Answer 1

Given :

Speed of the car = 144 km/hr = 40m/s

Distance travelled to stop the car = 200m

To Find :

Time taken dor the car to stop

Solution :

• From equations of motion  v² - u² = 2as

• By substituing the values in above equation

           v² - u² = 2as

           0 - 40² = 2×a×200

          400a = -1600

          a = -4 m/s²

• we also know ,v = u+at

          0 = 40 + (-4)t

          4t = 40

          t = 10sec

The time taken by the car to stop is 10 sec

     

Answer 2

Answer:-

The car takes 10 seconds to stop.

$\rule{200}{1}$

Given:-

• Initial velocity (u) = 144 km/h
• Distance (s) = 200 m

To find:-

• Time taken to stop (t) = ?

Solution:-

Here, as the car will stop so it's final velocity (v) = 0

And,initial velocity = 144 km/h

★ Changing velocity into m/s

→ u = (144 × 1000)/(60 × 60)

→ u = 144000/3600

→ u = 40 m/s

First we have to find acceleration so we will use this formula:-

☛ v² = u² + 2as

→ 0² = (40)² + 2a × 200

→ 0 = 1600 + 400a

→ 400a = -1600

→ a = -1600/400

→ a = -4 m/s²

Now we will find out time, so we will use this formula:-

☛ v = u + at

→ 0 = 40 + (-4)t

→ 0 = 40 - 4t

→ 4t = 40

→ t = 40/4

→ t = 10 s

Therefore,

The car takes 10 seconds to stop.