On the planet Newtonia, a simple pendulum having a bob with mass 1.35kg and a length of 195.0cm takes 1.31s , when released from rest, to swing through an angle of 12.5 ^\circ, where it again has zero speed. The circumference of Newtonia is measured to be 51400 {\rm km}.
a. What is the mass of the planet Newtonia?