Question:

The change in the value of '$g$' at a height '$h$' above the surface of the earth is the same as at a depth '$d$' below the surface of earth. When both '$d$' and '$h$' are much smaller than the radius of earth, then which one of the following is correct ?

Updated On: Jul 29, 2022
  • $d=\frac{h}{2}$
  • $d=\frac{3h}{2}$
  • $d=2\,h$
  • $d=h$
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The Correct Option is C

Solution and Explanation

$g_{h}=g\left(1-\frac{2\,h}{R}\right)\,...\left(i\right)$ $g_{d}=g\left(1-\frac{d}{R}\right)\,...\left(ii\right)$ From Eqs. $\left(i\right)$ and $\left(ii\right)$, $g\left(1-\frac{2\,h}{R}\right)=g\left(1-\frac{d}{R}\right)$ $\Rightarrow 2\,h=d$
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Concepts Used:

Gravitational Potential Energy

The work which a body needs to do, against the force of gravity, in order to bring that body into a particular space is called Gravitational potential energy. The stored is the result of the gravitational attraction of the Earth for the object. The GPE of the massive ball of a demolition machine depends on two variables - the mass of the ball and the height to which it is raised. There is a direct relation between GPE and the mass of an object. More massive objects have greater GPE. Also, there is a direct relation between GPE and the height of an object. The higher that an object is elevated, the greater the GPE. The relationship is expressed in the following manner:

PEgrav = mass x g x height

PEgrav = m x g x h

Where,

m is the mass of the object,

h is the height of the object

g is the gravitational field strength (9.8 N/kg on Earth) - sometimes referred to as the acceleration of gravity.