Q.

What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R       [2012]

1 5GmM6R  
2 2GmM3R  
3 GmM2R  
4 2GmMR  

Ans.

(1)

As we know,

Gravitational potential energy=-GMmr

and orbital velocity, v0=GMR+h

Ef=12mv02-GMm3R=12m·GM3R-GMm3R

     =GMm3R(12-1)=-GMm6REi=-GMmR+K

Ei=Ef

Therefore minimum required energy, K=5GMm6R