Question

A body travels $200cm$ in the first two seconds and $220cm$in the next 4 seconds. The velocity at the end Of the eleventh second is

• A. 0
• B. $10cm{s}^{-1}$
• C. $82cm{s}^{-1}$
• D. $100cm{s}^{-1}$

Answer 1

The correct option is B $10cm{s}^{-1}$

We are assuming that the body is under uniform acceleration here. Then$,$ the total distance $d$ travelled after the first t seconds is given by

d=ut+1/23
=u1Where u is the initial velocity and a is the acceleration$.$ We put the values of these quantities for the first 2 seconds$:$

200=2u+2a200=2u+2a

where u is in $cm/s$ and a is in $cm/s.$

Then at the end of 6 seconds$,$ the total distance travelled is $200+220=$ $420$ cm$.$ So$,$

420=6u+18a420=6u+18a

Upon solving, this gives $u=115cm/s$ and $a=-15cm/s.$

So velocity at the end of $7$ seconds is given by$:$

v=u+atv=u+at$

$=115-105$ = 10 cm/s

Hence,

option $\left(B\right)$ is correct answer.