## Activity Based Physics Thinking Problems in Mechanics: Universal Gravitation |

- the position of the space ship when it is at A and B;
- the velocity of the space ship when it is at A and B
- the acceleration of the space ship when it is at A and B.
1) Someone once stopped me in the hall and said: "I can prove Newton's theory of gravity is wrong. The sun is 320,000 times as massive as the earth, but only 400 times as far from the moon as the earth is. Therefore the force of the sun's gravity on the moon should be twice as big as the earth's and the moon should go around the sun instead of around the earth. Since it doesn't, Newton's theory of gravity must be wrong!" What's the matter with this reasoning? 2) The next problem uses the computer program ORBITS *. Run ORBITS and select the scenario SPSTATN (Space Station). This features a space ship in the same circular geosynchronous as a space station. Unfortunately, it is in orbit one-fourth of an orbit behind a space station. You want to rendezvous with the station by matching position and velocity with it. Try to rendezvous with the station by adding or subtracting velocity
(thrust) to your space ship using the + key to control the amount of thrust
and the arrow keys on the numeric keypad to control the direction (of D To view how closely you've rendezvoused, when you are satisfied, press<Ctrl><F2> to record your final positions and velocities to the data tables. Return to the data tables by pressing <BACKSPACE>. Press <PrtSc> to print out the exact values of the x and y positions and the x and y velocities of the space ship and space station. Calculate your distance from the space station and the relative velocity between you and the space station using the Pythagorean theorem. 3) The orbiting Hubble telescope was recently repaired by a crew of
astronauts from the Space Shuttle
5) Suppose you are piloting the space ship in the problem above and that the point at A is at a distance of 3 earth radii from the earth's surface, and the point B is at a distance of 1 earth radius from the center. You are at point A and want to change your orbit. (a) What would happen to the shape of your orbit if you decided to speed
up in the direction you are heading by firing your aft rockets briefly? 6) Two schoolmates, Romeo and Juliet, catch each other's eye across a crowded dance floor at a school dance. Estimate the gravitational attraction they exert on each other. |

* This software may be obtained from Physics Academic Software

These problems written and collected by E. F. Redish. These problems
may be freely used in classrooms. They may be copied and cited in published
work if the *Activity Based Physics Thinking Problems in Physics site*
is mentioned and the URL given. Web page edited by K.A. Vick.

To contribute problems to this site, send them to redish@physics.umd.edu.

Go back to the Thinking Problems page

Go back to the Thinking Problems in Mechanics page

Maintained by
University of Maryland PERG

Comments and questions may be directed to
E. F. Redish

Last modified June 21, 2002