Question

A particle moves in a straight line with a constant acceleration. It changes its velocity from $10 ms^{-1}$ to $20ms^{-1}$ while passing through a distance $135\, m$ in $t$ second. The value of $t$ is

• A. 10
• B. 1.8
• C. 12
• D. 9

Answer 1

Answer: (D)

$v^{2}-u^{2}=2 \, a s$
Given $v=20\, ms ^{-1},$
$ u=10 \,ms ^{-1}, $
$s=135 \,m$
$\therefore a=\frac{400-100}{2 \times 135}=\frac{300}{270}$
$=\frac{10}{9} \,m / s ^{2} $
$v=u+a t $
$\Rightarrow t=\frac{v-u}{a}=\frac{10\, m / s }{\frac{10}{9}\, m / s ^{2}}$
$=9\, s$