Question

A can filled with water is revolved in a vertical circle of radius $4\,m$ and the water does not fall down. What must be the maximum period of revolution?

• A. 2 sec
• B. 4 sec
• C. 1 sec
• D. 6 sec

Answer 1

Answer: (B)

4 sec

Answer 2

When a cone filled with water is revolved in a vertical circle, then the velocity at the highest point is given by
$v \geq \sqrt{g r}$
Also $v=r w=r \frac{2 \pi}{T}$
Hence, $\frac{2 r \pi}{T} \geq \sqrt{r g}$
$T \leq \frac{2 \pi r}{\sqrt{r g}}=2 \pi \sqrt{\frac{r}{g}}$
$=2 \pi \sqrt{\frac{4}{9.8}}$
$=2 \times 3.14 \times 0.6389$
$=4.0\, \sec$
So, $T_{\max }=4 \sec$