A body covers 12 m in 2nd second and 20 m in 4th second . Find what distance the body will cover in 4 seconds after the 5th second.

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Solution

Given :
Case I:
let initial velocity = u m/s
distance=s=12m
Time =t=2sec
S=u+a(2t-1)/2
12=u+a(2x2-1)/2
12=u+3a/2
2u+3a=24--------------(1)

Case II:
Time=t=4sec
distance =s=20m
20=u+a(2x4-1)/2
20=u+7a/2
2u+7a=40--------(2)
from 1 and 2:
2u+3a=24
2u+7a=40
- - -
***********
-4a=-16

a=4m/s^2

substitute the value of a in equation 1 we get :

u=6m/s
Case iii:
Now, distance covered in 4sec after 5second=distance covered in 9th sec-distance covered in 5 sec
=(6x9+1/24x9x9)-(6x5+1/245*5)
=54+162-(30+50)
=136m

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