Question:

A small body of mass $m$ slides without friction from the top of a hemisphere of radius $r$. At what height will the body be detached from the centre of the hemisphere?

Updated On: Jul 5, 2022
  • $\frac{r}{3}$
  • $\frac{r}{2}$
  • $\frac{2}{3}r$
  • 2r
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The Correct Option is C

Solution and Explanation

Body will be detached if $\frac{m \nu^{2}}{r}=m g \cos \theta$ As $\nu^{2}-0^{2}=2 g d$ $\nu=\sqrt{2 g d}$ and $\cos \theta=\frac{h}{r}$ So, from E (i), $\frac{m \times 2 g d}{r}=m g \frac{h}{r}$ or $h=2 d$ or $h=2(r-h)$ ie, $h=(2 / 3) r$
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Concepts Used:

Motion in a Plane

It is a vector quantity. A vector quantity is a quantity having both magnitude and direction. Speed is a scalar quantity and it is a quantity having a magnitude only. Motion in a plane is also known as motion in two dimensions. 

Equations of Plane Motion

The equations of motion in a straight line are:

v=u+at

s=ut+½ at2

v2-u2=2as

Where,

  • v = final velocity of the particle
  • u = initial velocity of the particle
  • s = displacement of the particle
  • a = acceleration of the particle
  • t = the time interval in which the particle is in consideration