assignment6solutions - Physics 161, section 02 Hammer...

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Unformatted text preview: Physics 161, section 02 Hammer Assignment 6 Due Oct 23, start of class Reference reading: One most week focused specifically on Newtons Laws (really the whole course is focused on Newtons Laws), now specifically around circular motion, in particular the ideas of centripetal force and acceleration. 1) Ive been telling you all along to come up with new problems to test your understanding, because you should never believe you understand an idea until you can use it in some new situation. In lecture last time, (Thursday Oct 11) I gave you a problem about me sitting on a seat heres my shot at a picture of that, only a little better than on the board. So if the swing seat and I together weigh about 1000 N , about 80% of the class figured that would be the force I exert downward on that rope so as not to fall. I explained why the answer is 500 N , and why it isnt 1000 N Maybe that problem now feels like it makes sense (and if it doesnt you should be asking questions!), but what you need to do is come up with another problem around these same ideas and see if you can solve it. Thats what Im asking you to do for this question what you should be do is exactly the kind of thing I do to write questions on exams. I think what can I ask them to find out if they really understood that question? Note that this problem itself is a variation of other problems weve done e.g. assignment 4, problems 4-6 have things in common with this; so do assignment 5 problem 3-4, and even 1 and 2. And Brian will do more on Tuesday. So dont feel as though theres a narrow range of questions that are fair game. Well, theres obviously no right answer for me to post for this one! So heres a variation to that question: Suppose that instead of just sitting there, Im pulling on the rope and lifting myself and the swing seat. And lets solve it for the idealized situation of rope with negligible mass and pulley with negligible mass and friction. To make that a bit more specific, suppose the seat and I are rising at a speed of 0.2 m/s , and that together we still have a weight of 1000 Newtons . What would be the tension in the rope then? (If thats not enough information, what other information would we need?) Thats my revised problem! Ill post the answer to it later. 2) Same as question 1, but for this problem, work a problem someone else wrote. This way you can check your answers: Find someone with whom to trade questions (you could use the Discussion board on Blackboard for this post your question, look for someone else posting theirs). If you dont come up with the same answers, or if youre not sure whether youre right, then that gives you questions to ask your TA or me!...
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This note was uploaded on 04/07/2008 for the course PHYS 161 taught by Professor Hammer during the Fall '07 term at Maryland.

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assignment6solutions - Physics 161, section 02 Hammer...

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