Question

A body travels $200m$ in the first two second and $220m$ in the next four second. The velocity at the end of the seventh second from the start will be

• A. 10 $m{s}^{-1}$
• B. 15 $m{s}^{-1}$
• C. 220 $m{s}^{-1}$
• D. 5 $m{s}^{-1}$

Answer 1

The correct option is A 10 $m{s}^{-1}$

$200=u\left(2\right)+\frac{1}{2}\times a(2{)}^2=2u+2a=200$
$\Rightarrow u+a=100-\left(1\right)$

Distance in next $4sec$ $\Rightarrow s_6-s_2$
$\Rightarrow 220=\left(u\right(6\left)\right]+\frac{1}{2}a\left(6{)}^2\right)-\left(u\right(2)+\frac{1}{2}a(2{)}^2)$
$420=6u+18a-\left(2\right)$
$420=6(100-a)+18a\left(from1\right)$
$\Rightarrow -180=12a\Rightarrow a=-15m/s^2,u=115m/s$

$v\left(atendof7sec\right)=u+at$$=115+(-15\times 7)=10m/s$