Question

At a certain acceleration, a racing car takes $5s$ to double its speed while moving at $2m{s}^{-1}$. If now, it moves at $4m{s}^{-1}$, at the same acceleration, what time will it take to double its speed?

• A. $5s$
• B. $10s$
• C. $15s$
• D. None of these

Answer 1

Answer: (B)

$10s$

Let the acceleration be $a$.
$v=u+at$
$4=2+(a\times 5)$
$a=\frac{2}{5}m{s}^{-2}$
Let the time required be $T$.
$\therefore 8=4+(\frac{2}{5}\times T)$
$4=\frac{2}{5}\times T$
$T=10s$