Question Details

The loss in weight of a body taken from earth's surface to a height h is 1%. The change in weight taken into a mine of depth h will be

Options

A

1% loss

B

1% gain

C

0.5% gain

D

0.5% loss

Correct Answer :

0.5% loss

Solution :

The correct option is 0.5% loss.

Let us analyze the variation of acceleration due to gravity with height and depth. Let g be the acceleration due to gravity on the surface of the Earth.

Case 1: At a height h above the Earth's surface
When a body is taken to a height h (where hR, and R is the radius of the Earth), the acceleration due to gravity gh is given by the approximation:
gh=g1-2hR

The weight of the body of mass m at height h is Wh=mgh, and its weight on the surface is W=mg.
The fractional change in weight (loss in weight) at height h is:
W-WhW=g-ghg=2hR

Given that the loss in weight at height h is 1%:
2hR=1%=0.01
This gives:
hR=0.5%=0.005

Case 2: At a depth h in a mine
The acceleration due to gravity at depth d=h is given by:
gd=g1-hR

The fractional change in weight (loss in weight) at depth h is:
W-WdW=g-gdg=hR

Substituting the value of hR from Case 1:
W-WdW=0.5%

Since the value is positive, it represents a decrease in acceleration due to gravity, which means there is a 0.5% loss in weight.

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