[Tycho?] Posted September 30, 2005 Share Posted September 30, 2005 That is the graph of the velocity of the rotating object. True or False: A) At time t_3, the magnitude of the tangential acceleration of a point on the rim of the disc is as large as it gets. B) According to convention, the disc rotates counter-clockwise during the interval from t_1 to t_2. C) At time t_3, the radial acceleration of a point on the rim of the disc is zero. D) At time t_2, the angular velocity of the disc is as large as it gets. E) At time t_3, the magnitude of the radial acceleration of a point on the rim of the disc is as large as it gets. F) The acceleration of a point on the rim of the disc points to the axis of the disc at time t_1. I just can't get this darned thing right. I have multiple guesses since its an online assingment, but I obviously am confused about something. I've tried looking up unfamiliar terms like "tangenital acceleration" and the like, but I still get something wrong. (If I get a single wrong, I get the entire question wrong, and so I dont know which or how many individual questions I got wrong) Help would be appreciated. Link to comment Share on other sites More sharing options...
mezarashi Posted October 1, 2005 Share Posted October 1, 2005 I'm sure this will be easy if you have the equations clarified: 1. tangential acceleration = change in angular velocity over time (hint: slopes of the graph) 2. radial acceleration = (angular velocity)^2 x radius (hint: since r is constant its proportional to the square of the angular velocity) Lastly, total acceleration = radial acceleration (towards center) + tangential acceleration (tangent to rim). (hint: last question, if either is non-zero, you won't get a perfect radial or tangential vector) Link to comment Share on other sites More sharing options...
[Tycho?] Posted October 1, 2005 Author Share Posted October 1, 2005 I love you. I even tried looking up radial acceleration, but I couldn't find a concise definition, thanks a bunch. If you're feeling generous you could help me with but a single other one. This one is so easy that I can't get it, and I dont know why. There is an object, who's velocity changes from 3m/s to 2m/s in 4 seconds, giving an average acceleration of -0.25m/s^2. I know the accleration is correct, becuse it was the answer to a question which I got right. The mass of this object is 162 grams. What is the average force over these four seconds? I get F= -0.0405 by multiplying average acceleration times mass. I dont see how this is wrong, so I've tried putting in other values, dividing by 4, making it positve, just doing junk with it. I really have no idea how this is wrong, it could just be I've been working on it for so long there is something obvious that I am unable to see. Link to comment Share on other sites More sharing options...
mezarashi Posted October 1, 2005 Share Posted October 1, 2005 ']There is an object' date=' who's velocity changes from 3m/s to 2m/s in 4 seconds, giving an average acceleration of -0.25m/s^2. I know the accleration is correct, becuse it was the answer to a question which I got right. The mass of this object is 162 grams. What is the average force over these four seconds? I get F= -0.0405 by multiplying average acceleration times mass. [/quote'] I don't know about this one. Using the momentum form of Newton's second law, you would still get the same answer. Maybe it's with the minus sign? F x t = m x (change in velocity) But honestly your answer seems correct... oh, and you're welcome Link to comment Share on other sites More sharing options...
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