Question

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

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

Answer 1

Answer: (C)

$s_1=40m,s_2=70m$
$\Delta t_1=5s,\Delta t_2=5s$
$40=u\left(\Delta t_1\right)+\frac{1}{2}a{\left(\Delta t_1\right)}^2=5u+\frac{1}{2}a\times 25$
$\Rightarrow 2u+5a=16$
$110=u\left(\Delta t_1+\Delta t_2\right)+\frac{1}{2}a{\left(\Delta t_1+\Delta t_2\right)}^2$
$110=10u+\frac{1}{2}a\times 100$
$\Rightarrow u+5a=11$
$u=5m{s}^{-1}$