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Tuesday, October 12, 2010
Ch8 1 #4
This problem is very much like the previous problem and uses the same basic ideas. Do you see why?
17 comments:
Anonymous
said...
shouldn't we use the equation a=(v^2)/r solve for the centripetal acceleration?
For part (B), a = v^2/r is correct - it's the centripetal acceleration.
For part (A), though, the *tangential* acceleration is requested. This is given in terms of the angular acceleration alpha by eqn. 8.6, and alpha can be gotten from it's basic definition in eqn. 8.4. (Do you see how eqn 8.4 for angular acceleration looks like the equation for linear acceleration?)
for part 2 I did v^2/r, it doesn't work? 2000 RPM / 60 to = 33.333 RPS, sub in for v = 2r*pi*f, then did v^2/r, and got about 1750 but it's incorrect? I used .04 m for the given 8.0 cm for radius.
I don't how to set up the actual equation, but I thought, if the tangential acceleration throughout the first 0.50 seconds was 17 m/s^2 (or whatever it comes out to be), then at 0.25 seconds the speed should be 1/4 of that value. That's how I found the speed and I plugged it into v^2/r and got around 440 m/s^2.
I don't how to set up the actual equation, but I thought, if the tangential acceleration throughout the first 0.50 seconds was 17 m/s^2 (or whatever it comes out to be), then at 0.25 seconds the speed should be 1/4 of that value. That's how I found the speed and I plugged it into v^2/r and got around 440 m/s^2.
For part (c), you first need to understand whether the time duration is during or after the acceleration ends. If it's during the acceleration, then eqn 8.7 (with angular acceleration, not linear) is it. If it's after the acceleration ends, then it's a two part problem, with the first period using 8.7 with non-zero alpha and in the second period with non zero omega, but zero alpha.
for part C, keep in mind that the answer they are looking for is in terms of total rads, so dont divide by 2pi to cancel out the effects of full rotations
17 comments:
shouldn't we use the equation a=(v^2)/r solve for the centripetal acceleration?
i don't know how to go about this question is there any reference point in the notes i could look at?
For part (B), a = v^2/r is correct - it's the centripetal acceleration.
For part (A), though, the *tangential* acceleration is requested. This is given in terms of the angular acceleration alpha by eqn. 8.6, and alpha can be gotten from it's basic definition in eqn. 8.4. (Do you see how eqn 8.4 for angular acceleration looks like the equation for linear acceleration?)
i have been trying to do part C but I can't seem to get it. help!!!
for part 2 I did v^2/r, it doesn't work? 2000 RPM / 60 to = 33.333 RPS, sub in for v = 2r*pi*f, then did v^2/r, and got about 1750 but it's incorrect? I used .04 m for the given 8.0 cm for radius.
I don't how to set up the actual equation, but I thought, if the tangential acceleration throughout the first 0.50 seconds was 17 m/s^2 (or whatever it comes out to be), then at 0.25 seconds the speed should be 1/4 of that value. That's how I found the speed and I plugged it into v^2/r and got around 440 m/s^2.
I don't how to set up the actual equation, but I thought, if the tangential acceleration throughout the first 0.50 seconds was 17 m/s^2 (or whatever it comes out to be), then at 0.25 seconds the speed should be 1/4 of that value. That's how I found the speed and I plugged it into v^2/r and got around 440 m/s^2.
Can anyone help with part (C)? I can't figure it out.
Part C is really giving me an issue...i used equation 8.7 and 8.9...is that right? HELP
Did you remember to add the initial angular position, theta_0, in
theta = theta_0 + omega_0*t + (1/2)alpha*t*t?
Yeah. I changed the initial it to radians before using it
For part (c), you first need to understand whether the time duration is during or after the acceleration ends. If it's during the acceleration, then eqn 8.7 (with angular acceleration, not linear) is it. If it's after the acceleration ends, then it's a two part problem, with the first period using 8.7 with non-zero alpha and in the second period with non zero omega, but zero alpha.
(Follow up) Yes, 8.9 can also be used for part(C). Watch out for units and theta_0.
for part C, keep in mind that the answer they are looking for is in terms of total rads, so dont divide by 2pi to cancel out the effects of full rotations
can someone help me with part c? i keep getting 260 rad but its tellin me it is not the right answer
part c is not working for me at all
This question was way too difficult and unfair. I literally spent 45 minutes on it, then it wouldn't show me the answer!
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