Question

A body moving with uniform acceleration describes $40 \, m$ in the first $5 \, s$ and $70 \, m$ in the next $5 \, s$ . Its initial velocity will be

• A. $4 \, m \, s^{- 1}$
• B. $2.5 \, m \, s^{- 1}$
• C. $5ms^{- 1}$
• D. $11 \, m \, s^{- 1}$

Answer 1

Answer: (C)

$s_{1}=40 \, m, \, s_{2}=70 \, m$
$\Delta t_{1}=5 \, s,\Delta t_{2}=5s$
$40=u\left(\Delta t_{1}\right)+\frac{1}{2}a\left(\Delta t_{1}\right)^{2}=5u+\frac{1}{2}a\times 25$
$\Rightarrow 2u+5a=16$
$110=u\left(\Delta t_{1} + \Delta t_{2}\right)+\frac{1}{2}a\left(\Delta t_{1} + \Delta t_{2}\right)^{2}$
$110=10u+\frac{1}{2}a\times 100$
$\Rightarrow u+5a=11$
$u=5ms^{- 1}$