Question

A body travels $200cm$ in the first two seconds and $220cm$ in the next four seconds. What will be the velocity at the end of $7^{th}$ second from the start?

• A. $10cm{s}^{-1}$
• B. $20cm{s}^{-1}$
• C. $15cm{s}^{-1}$
• D. $5cm{s}^{-1}$

Answer 1

Answer: (A)

$10cm{s}^{-1}$

$s=ut+\frac{1}{2}a{t}^2$
For $case1.$
$200=2u+2a$
$u+a=100....\left(1\right)$
For $case2.$ .i.e. next 4 seconds, we have distance $=420cm$ and time $=6s$
$420=6u+18a$
$u+3a=70....\left(2\right)$
Solving equation $1$ and $2,$ we get,
$u=115cm/s$ and $a=-15cm/s^2$
Now by
$v=u+at$
$v=115-15\times 7$
$v=10cm/s$
Hence answer is A.