13–117. Prove Kepler’s third law of motion. Hint: Use Eqs. 13–19, 13–28, 13–29, and 13–31.
Prob. 13–120
13–121. The rocket is in free flight along an elliptical trajectory A 'A . The planet has no atmosphere, and its mass is 0.70 times that of the earth. If the rocket has an apoapsis
and periapsis as shown in the figure, determine the speed of the rocket when it is at point A.
13–123. The rocket is initially in free-flight circular orbit around the earth. Determine the speed of the rocket at A. What change in the speed at A is required so that it can
move in an elliptical orbit to reach point A '?
*13–124. The rocket is in free-flight circular orbit around the earth. Determine the time needed for the rocket to travel from the innner orbit at A to the outer orbit at A '.
A
A A¿ A¿
Probs. 13–123/124
Prob. 13–121
