Question

Starting from a stationary position, Bhuvan paddles his bicycle to attain a velocity of 6m/s

in 30s. Then he applies brakes such that the velocity of bicycle comes down to 4m/s in the

next 5s. Calculate the acceleration of the bicycle in both the cases.

Answer 1

HI !

Case I 
============
Initial velocity = u = 0
Final velocity = v = 6 m/s
Time = t = 30 sec

Acceleration = a 

a = v-u/t
   = 6 - 0/30
   = 0.2 m/s²
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Case II
------------
Initial velocity = u = 6 m/s
Final velocity = v = 4 m/s
Time = t = 5 sec

a = v-u /t
   = 4-6/5
   = -2/5
   = -0.4 m/s²

The acceleration is negative, which indicates retardation 

Answer 2

for 1st case :
initial velocity of Bhuvan = 0 m/s
velocity after 30 sec = 6m/s
we know,
acceleration = change in velocity/ time taken
= { final velocity - initial velocity}/time taken
= ( 6 - 0)/30 = 6/30 = 0.2 m/s²

for 2nd case :-
initial velocity = 6 m/s
velocity after 5 sec = 4 m/s
acceleration = ( final velocity- initial velocity )/time taken
= ( 4 - 6)/5 = -2/5 = -0.4 m/s²

hence Bhuvan in first case accelerated with 0.2 m/s² and in 2nd case retardated with 0.4 m/s² .