A body travels 200 cm in the first 2 s and 220 cm in the next 4 s with deceleration. The velocity of the body at the end of the seventh second is

$\begin{array}{l}200=u\times 2-(1/2)a(2{)}^2\\ \text{ or }u-a=100 ....\left(i\right)\\ 200+220=u(2+4)-(1/2)(2+4{)}^{2}a\\ \text{ or }u-3a=70 ....\left(ii\right)\end{array}$

$\text{ Solving Eqs (i) and (ii), we get }a=15{\mathrm{cms}}^{-2}\text{ and }u=115{\mathrm{cms}}^{-1}\text{. }$

$\text{ Further, }v=u-at=115-15\times 7=10{\mathrm{cms}}^{-1}$