Please make comments about what the correct choice to this question is, and explain why. Also, change "the period of one year" to "one month," and then answer the same question.
Monday, October 27, 2008
QR: The Sun doing any work on the Earth?
Hi, this is "quiz revisited" for today's quiz. The question that I select is the last one, because I want to make sure that everyone understands the solution to this.
Please make comments about what the correct choice to this question is, and explain why. Also, change "the period of one year" to "one month," and then answer the same question.
Please make comments about what the correct choice to this question is, and explain why. Also, change "the period of one year" to "one month," and then answer the same question.
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3 comments:
The correct answer is zero because the force is perpendicular to the motion. When looking at the work the sun does the cos of 90 degrees is zero and makes the work equate to zero.
Now that the problem has changed, we can no longer say that the displacement of the earth around the sun is zero, and therefore work is zero (which was actually my first guess). Remember, we are using the equation W=|F||delta,r|cos@ (where F and r are both vectors to determine the amount of work done. Now that displacement is in fact non-zero we must look at the force of the sun on the earth and the direction of that force in order to determine whether or not the work the sun does on the earth is negative, positive, or zero.
Since the earth travels in a circle around the sun, and therefore accelerating, we can conclude that the sun indeed exerts a force of gravity on the earth. So |F| in non-zero.
Whats left to determine is the direction of the force the sun exerts on the earth and use this to determine what work is done. Because the earth travels in a circle around the sun the force of gravity the sun exerts on it is always perpendicular to the earths motion. Because cos(90')=0, we can conclude that the work the sun does on the earth is zero.
Thanks, Sharon and Abram. You guys both got bonus for your good comments.
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