Question

A bus moving with a speed of 54 km/h. On applying brakes, it stopped in 8 seconds. Calculate the acceleration and the distance travelled before stopping.

Answer 1

According to the question,
Initial Velocity of bus = 54 km/h = 54 X 5/18 = 15 m/s
Final Velocity of bus = 0 (As brakes are applied and bus gradually comes to rest)
Time taken to reach the Final Velocity = 8 seconds
Acceleration = v - u / t
a = 0 - 15 / 8
Retardation =  - 1.875 m/s²
For calculating Distance,  S = u X t + 1/2 at²
S = ( 15 X 8 ) + 1/2 X -1.875 X 8²
S = 120 + ( -120/2 )
S = 120 + (- 60)
S = 120 - 60
Distance travelled by the bus before stopping = 60 metres

Answer 2

Concept:

• 1 D motion
• Speed
• Acceleration
• Kinematics

Given:

• Initial speed = 54km/h = 15m/s
• Stopping time t = 8s

Find:

• Acceleration
• Distance travelled before stopping

Solution:

Final speed v = 0, as the bus has stopped

We know the equation, v = u+at

v = u+at

0 = 15 + a (8)

a = -15/8 = -1.875m/s^2

s= t(v+u)/2

s = 8 (0+15)/2 = 60m

The acceleration is 1.875m/s^2 and the distance travelled before stopping is 60m.

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