(a) What is Earth's gravitational acceleration on an object on its surface?  
Remember that the mass of Earth is approximately 5.98 * 10^24 kg, and its radius 
is approximately 6.38 * 10^6 m.

(b) What is the Sun's gravitational acceleration on Earth?  Remember that the 
distance between Earth and the Sun is one astronomical unit (1.5 * 10^11 m), and 
that the mass of the Sun is approximately 2.0 * 10^30 kg.