Sun July 24, 2011 By:

A body travels a distance of 2m in 2s and 2.8m in next 4s. What will be the speed of the body at the end of the 10th second from start?

Expert Reply
Mon July 25, 2011
case (i) S=2m , t=2s
case(ii) S=2+2.8=4.8m  ,t=2+4=6s
let u and a be the initial velocity and uniform acceleration of the body.
we know that, S=ut+1/2 a
case(i),  2=ux2+1/2 ax or
             1=u+a     (i)
case(ii),  4.8=ux6+1/2 ax
             0.8=u+3a  (ii)
subtracting (ii) from (i), we get
            0.2=0-2a=-2a  or a=-0.2/2=-0.1m/
   put the value of 'a' in (ii) ,we get
          0.8=u+3x (-0.1)
          u=1.1 m/s
for the velocity of body at the end of10th second, we have
u=1.1m/s  ; a=-0.1m/s2 ,v=? ,t=10 s
as ,v=u +at
hence, v= 1.1 +(-0.1)x10=1.1-1= 0.1m/s
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