The correct answer is option 4) i.e. ∞
CONCEPT:
- The time period of a pendulum is given by the equation:
\(\Rightarrow T = 2\pi\sqrt{\frac {L}{g}}\)
Where L is the length of the string of pendulum and g is the acceleration due to gravity.
EXPLANATION:
- At a height of 900 km from the earth's surface gravity is absent.
Therefore, g = 0.
Substituting g = 0,
\(\Rightarrow T = 2\pi\sqrt{\frac {L}{0}} = ∞\)
Thus, the time period of the pendulum at a distance of 900 km from the Earth will be infinite.


