Question

A body travels $200cm$ in the first two seconds and $220cm$ in the next $4s$ with same acceleration.The velocity of the body at the end of the $7^{th}$ second is

• A. $5cm/s$
• B. $10cm/s$
• C. $15cm/s$
• D. $20cm/s$

Answer 1

The correct option is B $10cm/s$

$200=u\times 2+\frac{1}{2}a(2{)}^2$

$100=u+a..........\left(i\right)$

$420=u\left(6\right)+\frac{1}{2}a(6{)}^2$

$70=u+3a..........\left(ii\right)$

from $\left(i\right)$ and $\left(ii\right)$ $2a=-30\Rightarrow a=-15cm/s^2$

$\therefore u=100-a=100-(-15)=115cm/s$

$u_{7^{th}}=u+at=115+(-15)\left(7\right)=115-105=10cm/sec$