Q13 of 47 Page 8

A bus decreases its speed from 80 km h-1 to 60 km h-1 in 5 s. Find the acceleration of the bus.

When a moving vehicle decreases its speed by applying breaks, the phenomenon is called de-acceleration.

Firstly, we will change the speed from km/h to m/s, as the given time is in seconds.

Initial speed, u = 80 km/h (Given)

(We know 1km=1000m and 1hour=3600 seconds)

=

= 22.22 m/s (i)


Final speed of bus, v = 60 km/h(Given)

(We know 1km=1000m and 1 hour=3600 seconds)

=

= 16.67 m/s (ii)


Time taken, t = 5 sec (iii)

As we know, from first equation of motion that v= u + a × t

Acceleration, a =


Putting the Values from (i) ,(ii) and (iii)

a =
a =

a = - 1.11 m/s2

Here, negative sign shows the retardation in the sped off bus due to application of brakes.

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