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these are not answers to your questions. i am sorry for the misunderstanding. i have been posting answers to the even numbered problems which are randomized for each student. this is the helping device to student. it is not meant to give the answer itself. it was explained in one of the previous blogs. i started doing it from requests of couple of students. these are answers to textbook version questions. the idea is that you figure out the procedure to do the problem using the textbook numbers, cross-check your answers with these, and then move on to calculate the answer for the MP questions.
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Hint on 9.31 (how to do it without moving your hand)
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In today's (Dec. 3) class, I told you that the 1D elastic collision with m much less than M corresponds to 9.31. Here m is the mass of the ball. M is the mass of the car.
However, note that M is not at rest initially, in 9.31, as opposed to what we did in lecture. How can we still make use of what we did in class?
(1) Convert the velocity of the ball, as reference to the moving frame of the car. (2) In the moving frame of the car (i.e. from the driver point of view), the car is always at rest, so what we did in class is applicable. So, figure out what is the final velocity of the ball within that frame. That was a very simple result! (3) Convert the velocity back to the child's rest frame velocity.
These calculations are mouth-fuls to describe, but they are simple enough so you could do them in your head, in principle.
Or, you could just set up the momentum conservation equation (where you would neglect certain terms based on masses), and that "grand result equation" for 1D elastic collision: v1i - v2i = v2f - v1f, and then just solve them.
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9.12: 75 cm from the center
9.76: 0.33 J
13.64: (a) 6.5 cm, (b) 0.51 s
Good luck!!
13.64: (a) 6.5 cm, (b) 0.51 s
Good luck!!
Please note -- this homework is due on Thursday, the 4th, and no late homework will be accepted. This is so that we can move on to the final exam, as smoothly as we can.
10 comments:
Is it correct that it is due on Wed instead of Thurs?
Sorry about that. It is due on Thursday, as usual. This has been corrected.
However, what is unusual about this homework would be that no late homework will be accepted .
For problem 9.66, I got the correct answer for the first two parts. And I know that the answer for part c should have the same numbers as part b, but with a different sign. However, the computer does not accept my numbers for part c. Does anybody have any ideas as to why part c would need different coefficients?
J. Quinn, what you did is completely correct! It seems that the problem is that possible answers in the MasteringPhysics program are more complete in part B than in part C. I just reported this problem to MasteringPhysics. They should include your answer as a correct one, by Tuesday, I think. I will check to give you the correct credit when you are done.
please reference prob 9.76
Ive attempted two methods
inelastic collision conserves momentum where velocity of block is initially zero and finally it is equivalent to K=U. So if all else is known then reducing algbraically until the final veloicty of pellet emerges. I fail to attain a good answer using v final to solve for Kremain.
conservation of energy
Kpellet = Ublock + Kremain
still nothing, both answer already in joules.
Hello?
genevra: should the energy be conserved here during the collision? this problem is the same kind as the normal ballistic pendulum problem in the sense that the momentum is conserved, and only that, during the collision. i.e., your first approach seems ok, from as much as i can tell from your description. however, i am not clear on what you actually did. see the above posting with the answer to the book question, maybe that will help?
By late do you mean anytime after 9am on thursday or if we turned it in like 5pm of thursday would that still be thought as late?
casanj: yes, after 9am would be late. we should move on to reviewing the homework, after i load my solutions at that time. i think this is the best for most students. the final is on the 8th!
I tried using Energy=.5mv^2 to solve for v before it hit the block. However, when I plug in the numbers I get a pellet that is going over 111 m/s. This doesn't seem right yet it does if my formula is correct. What am I doing wrong? This is for problem 9.76.
i don't think anything is wrong there, really.
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