Question

a bady moving with 20m/s comes to rest in 5sec find the retardation

Answer 1

here ,initial velocity of baby is 20m/s
and, final velocity is 0m/s
time is given as 5 seconds.
hence, retardation = (final velocity- initial velocity)/time
=( 0-20)/5
-20/5
=-4 m/s

Answer 2

Hii..

As body comes to rest , final velocity ( v ) = 0 m/s
and , initial velocity (u ) = 20 m/s [ given ]

a/c to first eqn of motion, v = u + at

=> 0 = 20 + (-a ) 5 [ retardation = negative accn.]

=> - 20 = -5a

=> a = 4 m/s

and , retardation = -a
so, retardation = -4 m/s

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hope this helps !