Question

A body starts from rest and attains a velocity of 12m/s in 30 seconds. If the final velocity becomes 8m/s, what will be the deceleration after 5 seconds?

Answer 1

hey mate...

u=0 v=12m/S t=30 sec a=v-u/t =12-0/30 =12/30 =0.4m/s"2 N
ow retardation =v=8 m/S
u=12m/S t=S a=v-u/t
=8-12/5
=-4/5
=-0.8 m/s"2

Answer 2

The deceleration will be 0.8 m /s^2.

Given :

A body starts from rest and attains a velocity of 12m/s

Time = 30s

To find :

The deceleration after 5 secs when final velocity becomes 8m/s

Solution :

We know,

v = u + at

where v is final velocity , u is initial velocity , a is acceleration and t is the time taken

In the given question , v = 12 m/s , u = 0 m/s t = 30secs

Hence,

12 = 0 + a × 30

=> 12 = 30a

=> a = 12/30

=> a = 4/10

=> a = 2/5 m/s^2

On retardation ,

v = 8m/s

t = 5 s

u = 12 m/s

Hence, 8 = 12 + a×5

8 = 12 + 5a

=> 5a = 8 - 12

=> a = -4/5 ( negative sign indicates negative acceleration )

= 0.8

Hence , the deceleration will be 0.8 m /s^2.

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