- Find an expression for the minimum speed at which an object of
mass m must be launched in order to escape Earth’s gravitational
field. (This is called escape speed.)
Here’s How to Crack It
When launched, the object is at the surface of the earth (r 0 = rE) and has an upward,
initial velocity of magnitude v 0. To get it far away from the earth, we want to bring
its gravitational potential energy to zero, but to find the minimum launch speed, we
want the object’s final speed to be zero by the time it gets to this distant location.
So, by conservation of energy
which gives