A body covers 200 cm in the first 2s of motion and 220 cm in the next 4s. Calculate the velocity 7s after the start.

Explanation

We know, s = `ut + (1)/(2)at^(2)`
`:.` Putting t = 2 s
`200 = uxx2+(1)/(2)axx4 = 2u +2a`
or,`" "` u+a = 100
The displacement in (4+2) or 6s = 200 +200 = 420 cm
`:. " " 420 = uxx6+(1)/(2)axx36 = 6u + 18a`
or,`" "`u+3a = 70
From equations (1) and (2) we get,
`a = -15 "cm.s"^(-2)` and u = 115 `"cm.s"^(-1)`
Velocity after 7 s of motion,
`v = u+at = 115-15xx7 = 115-105 = 10 "cm.s"^(-1)`