Question

$P$ varies directly as cube of $r$. $P=26$ when $r=2$. When $r=4,P$ equals

• A. 208

Answer 1

The correct option is A 208
Given that $P\propto r^3$

$\Rightarrow P=k\times r^3$

Given: $P=26$ when $r=2$
$\Rightarrow 26=k\times 2^3$

$\Rightarrow k=\frac{26}{8}=\frac{13}{4}$

$\therefore P=\frac{13}{4}\times r^3$

Now, when $r=4$

$P=\frac{13}{4}\times 4^3=208$