Question

A body is moving with uniform acceleration. covers $200\, m$ in the first $2\, s$ and $220\, m$ in the next $4\, s$. Find the velocity in $m / s$ after $7\, s$.

• A. 10
• B. 15
• C. 20
• D. 30

Answer 1

Answer: (A)

10

Answer 2

Let the initial velocity $= u$ and acceleration $= a$
In first case $s_{1}=u t_{1}+\frac{1}{2} a t_{1}^{2}$
$200=2 u +2 a \left(\therefore t_{1}=2 s \right)$
$u + a =100$ ... (i)
In second case $s_{2}=u t_{2}+\frac{1}{2} a t_{2}^{2}$
$420=6 u +18\, a \left(\therefore t_{2}=2+4=6 s\right)$
$3 a + u =70$ ... (ii)
Solving Eqs. (i) and (ii), we get
$a =-15\, ms ^{-2}$
and $u =115\, ms ^{-2}$
$v = u + at$
$=115-15 \times 7=10\, ms ^{-1}$