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Motion In Straight Line

Question
CBSEENPH11017205

A body starts from rest and accelerates uniformly at rate α for time tand then retards instantaneously at the rate β for time t2 to come to rest. Show that the ratio of the time of accelerated motion to the time of retarded motion is equal to ratio of retardation to the acceleration.

Solution

For accelerated motion:
Initial velocity, u = 0 m/s
Acceleration =straight alpha m/s
Time taken = t1 sec 
Let, v be the velocity acquired by the body at the end of accelerated motion.
By using the relation,
v = u + at,
we have 
V = 0 + alpha t subscript 1 space equals space alpha t subscript 1       ...(1) 
For retarded motion, 
straight u space equals space straight V space space space space space space space straight alpha space equals space minus straight beta
straight t space equals space straight t subscript 2 space space space space space space space space space straight v space equals space 0 
Now, using this relation, v= u + at, we have
0 space equals space straight V space minus space beta t subscript 2 space
space space space straight V space equals space space beta t subscript 2 space space space space space space space space space space space space space... space left parenthesis 2 right parenthesis

So space from space equations space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis comma space we space have

alpha t subscript 1 space equals space beta t subscript 2 space

therefore space space alpha t subscript 1 space equals space beta t subscript 2 space
space space space space space space space space space
space space space space straight t subscript 1 over straight t subscript 2 space equals space straight beta over straight alpha