Engineers want to test a new cannon that provides a long-range projection.
What speed does a projectile need to orbit the Earth just above the ground when it is projected from the ground?
How much speed is needed for this projectile to completely leave the Earth's attraction?
What would be the mass of the Earth so that even a projectile that could reach the speed of light would not escape its gravity? The mass of the Earth is 
, its radius is 6400 km, and the speed of light is 
. Assume that the atmosphere has no effect on the projectile.
.
.
which is 
times the mass of the Sun.
