15. The Earth is assumed to be similar to a sphere of radius R=6400 km and mass Mo=6 10-4 kg. The gravitational constant is G=6.67 10-4 m2 kg's? (a) Calculate the value of the acceleration of gravity go at the surface of the Earth. Deduce the the acceleration of gravity gh at an altitude h in terms of go. R and h. (6) Calculate the gravitational acceleration at the solar surface and compare it with the gravitational acceleration at the surface of the Earth. [Mass of Sun=2X1050kg, Radius of the Sun=6.96X10% m). (c) Calculate the escape velocities of the Sun and the Earth