First slide
Variation of g
Question

The angular velocity of the earth about its polar axis so that the weight of the body at the equator will be zero is

Easy
Solution

\large {g_\phi } = g - R{\omega ^2}{\cos ^2}\phi
\large \Rightarrow 0 = g - {R^2}{\omega ^2} \Rightarrow \omega = \sqrt {\frac{g}{R}}
Now g = 10 m/s2  and R = 6400 km = 64 x 105 m/s2
\large \therefore 
ω = 1.25 x 10-3 rad/sec

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