8. Centripetal Forces & Gravitation

How much energy is required to move a 1000-kg object from Earth's surface to a height twice Earth's radius?

You launch a rocket with an initial speed of $5\times 10^3$ m/s from Earth's surface. At what height above the Earth will it have ¼ of its initial launch speed? Assume the rocket's engines shut off after launch.

A rogue band of colonists on the moon declares war and prepares to use a catapult to launch large boulders at the earth. Assume that the boulders are launched from the point on the moon nearest the earth. For this problem you can ignore the rotation of the two bodies and the orbiting of the moon. (a) What is the minimum speed with which a boulder must be launched to reach the earth?

Hint: The minimum speed is not the escape speed. You need to analyze a three-body system.

(II) For a satellite of mass in a circular orbit of radius r_S around the Earth, determine

(b) its potential energy U (U = 0 at infinity) , and

(II) Two Earth satellites, A and B, each of mass m = 950 kg , are launched into circular orbits around the Earth’s center. Satellite A orbits at an altitude of 4800 km, and satellite B orbits at an altitude of 12,600 km.

(a) What are the potential energies of the two satellites?