Question

12. A bus decreases its speed from 80km/hr to 60km/hr in 5sec. The
acceleration of the bus is
1) 10m/s* ) 5m/s* 3) 2m/s 4) 1.112m/s​

Answer 1

Answer:

We have to very careful with units while doing the numerical questions.

Here we would convert km/h into m/s

Initial Speed (u) = 80 km/h= (80 ×1000)/3600 m/s = 22.22 m/s

Final Speed (u) = 60 km/h= (60 ×1000)/3600 m/s = 16.66 m/s

Now

Acceleration is given by

= Change in speed/ time taken

= (v-u)/t

=-1.112 m/s

Here negative sign denotes de-acceleration

Explanation:

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Answer 2

Initial speed (u) = 80kmph = 80 X 5/18 m/s = 200/9 m/s

Final speed (v)  = 60kmph = 60 X 5/18 = 50/3 m/s

Change in speed = v - u = 50/3 - 200/9 = -50/9 m/s

Acceleration = Change in speed/time = (-50/9)/5 = -10/9 m/s^2

So the acceleration of the bus is -1.112 m/s^2

Or the bus is decelerating at a rate of 1.112 m/s^2

So the answer is (4)