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## 13 October 2010

### Gravitation and Newton's Third Law Quiz

We've just finished covering Universal Gravitation.  Last night, my class did a problem involving a geosynchrous satellite orbiting Jupiter... they were to calculate the altitude of the satellite, and compare that altitude to the radius of Jupiter.

Today's quiz deals with conceptual issues from this problem, and reinforces Newton's Third Law (which we've been hammering for a week now).  I particularly like the last question, the ranking task -- it forces students to think beyond a single force pair.  They must combine their understanding of gravitation AND the Third Law.

Note that this quiz can be given in longer form or as a homework problem, just by adding the phrase "justify your answer" to the end of each question.

Space probe A orbits directly above Jupiter’s red spot, 9000 km above the surface. Identical space probe B sits on the surface of Jupiter.

27. Which probe has the bigger period of revolution?
(A) Probe A
(B) Probe B
(C) Both have the same period

28. Which probe has the bigger speed?
(A) Probe A
(B) Probe B
(C) Both have the same speed

29. Which probe has the bigger acceleration toward the center of Jupiter?
(A) Probe A
(B) Probe B
(C) Both have the same acceleration

30. Rank the magnitudes of the following gravitational forces from greatest to least. If two or more quantities are the same, say so clearly.

I. the force of Jupiter on space probe A
II. the force of Jupiter on space probe B
III. the force of space probe A on Jupiter
IV. the force of space probe B on Jupiter
V. the force of space probe A on space probe B
VI. the force of space probe B on space probe A

greatest ___ ___ ___ ___ ___ ___ least

#### 1 comment:

1. I recently did the probe question with my AP Physics 1 class. However, there is a serious scientific flaw with this problem. The problem claims probe B sits on Jupiter's surface. I don't see how that's possible when Jupiter is a gas giant. It does not have a solid surface. It does have an atmosphere but the probe could not "sit on the surface." I probe would just continue to travel and get pulled towards its center of mass.