Question

Can a pendulum clock be used in an earth-satellite?

Answer 1

No. According to the relation:
$T=2\pi \sqrt{\frac{l}{g}}$
The time period of the pendulum clock depends upon the acceleration due to gravity. As the earth-satellite is a free falling body and its g_effective (effective acceleration due to gravity ) is zero at the satellite, the time period of the clock is infinite.