Question

Question 20
An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s.
What will be the velocity after 7 s from the start?

Answer 1

$s_1=ut+\frac{1}{2}a{t}^2$ or $20=0+\frac{1}{2}a(2{)}^2$ or $a=10m{s}^{-2}$
$v=u+at=0+(10\times 2)=20m{s}^{-1}$
$s_2=160=vt+\frac{1}{2}{a}^{\prime }(t{)}^2=(20\times 4)+(\frac{1}{2}{a}^{\prime }\times 16)\Rightarrow a^{\prime }=10m{s}^{-2}$
Since acceleration is the same, we have $v^{\prime }=0+(10\times 7)=70m{s}^{-1}$