Question

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

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

Answer 1

Answer: (B)

$200=u \times 2-(1 / 2) a(2)^{2}$
or $u-a=100$ ...(i)
$200+220=u(2+4)-(1 / 2)(2+4)^{2} a$
or $u-3 a=70$ ...(ii)
Solving Eqs (i) and (ii),
we get $a=15\, cm\,s ^{-2}$
and $u=115\, cm\,s ^{-1}$.
Further, $v=u-a t=115-15 \times 7$
$=10\, cm\, s ^{-1}$.