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Assuming the earth to be a sphere of uniform mass density, a body weighed \(300 \ N\) on the surface of earth. How much …

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Assuming the earth to be a sphere of uniform mass density, a body weighed \(300 \ N\) on the surface of earth. How much it would weigh at \(\frac{R}{4}\) depth under surface of earth ?

a

\(225 \ N\)

b

\(75 \ N\)

c

\(300 \ N\)

d

\(375 \ N\)

✓ Correct answer: a)

\(225 \ N\)

Explanation

For a uniform-density Earth, acceleration due to gravity at a depth d is

g_d=g\left(1-\frac{d}{R}\right)

Given:

\(d=\frac{R}{4}\)

Therefore,

\({g}_{d}=g(1-\frac{1}{4})\) \({g}_{d}=\frac{3}{4}g\)

Weight is proportional to g.

\({W}_{d}=300\times \frac{3}{4}\) \({W}_{d}=225\ \text{N}\)

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