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Homework 7, due October 13.
Posted: Fri Oct 09, 2015 2:08 pm
by goodwine
Reading: By now you should have read all of chapters 1 - 4 except section 1.6 from Chapter 1.
Exercises: 4.17, 4.19, 4.26 and 4.27.
For 4.26, x in the equation is the displacement of the end of the beam in the downward direction. It is NOT along the axis of the beam, as the figure indicates.
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 4:14 pm
by bkenned7
4.27 Part 3
How do we plot |x_p/r| ? The x_p that I calculated has multiple unknowns in it (mass and k). Guessing this is wrong?
Since it says to compare to Figure 4.5, is eccentricity equal to the magnification factor?
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 5:32 pm
by goodwine
bkenned7 wrote:4.27 Part 3
How do we plot |x_p/r| ? The x_p that I calculated has multiple unknowns in it (mass and k). Guessing this is wrong?
Since it says to compare to Figure 4.5, is eccentricity equal to the magnification factor?
Get it in terms of frequency ratio and then you should be able to plot it vs frequency ratio for various damping ratios, i.e., get it like the other magnification factor plots.
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 6:57 pm
by jmcgill1
4.27
Is there a damper in this problem or not? The problem statement says the motor is attached to a mass-spring-damper system, but Fig 4.33 doesn't seem to have a damper attached. Also were supposed to compare our plot to Figure 4.5, which corresponds to modeling systems with forced, undamped vibrations.
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 7:12 pm
by goodwine
jmcgill1 wrote:4.27
Is there a damper in this problem or not? The problem statement says the motor is attached to a mass-spring-damper system, but Fig 4.33 doesn't seem to have a damper attached. Also were supposed to compare our plot to Figure 4.5, which corresponds to modeling systems with forced, undamped vibrations.
No damper in the picture, so you can assume no damping. Yes, if your plot is any different, explain why and connect the answer to the physics of the problem.
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 7:25 pm
by ekearney
Are we to assume that the mass me and mass m are the same so that they cancel each other out for the steady-state ratio solution?
Re: Homework 7, due October 13.
Posted: Sun Oct 11, 2015 8:04 pm
by goodwine
ekearney wrote:Are we to assume that the mass me and mass m are the same so that they cancel each other out for the steady-state ratio solution?
No (and that should make some sense if you think what this problem is modeling).
Re: Homework 7, due October 13.
Posted: Mon Oct 12, 2015 1:30 pm
by mrosset1
For 4.26 do we take into account the force gravity has on the mass?
Re: Homework 7, due October 13.
Posted: Mon Oct 12, 2015 1:32 pm
by goodwine
mrosset1 wrote:For 4.26 do we take into account the force gravity has on the mass?
No, the point of the gravity problem in the last homework is that there is no need to do so.
Re: Homework 7, due October 13.
Posted: Mon Oct 12, 2015 8:53 pm
by kpulliam
For Problem 4.27 in part 3 it tells us to plot |xp/r| versus w/wn is the r in the |xp/r| the fixed distance or the ratio w/wn?
Re: Homework 7, due October 13.
Posted: Mon Oct 12, 2015 8:55 pm
by goodwine
kpulliam wrote:For Problem 4.27 in part 3 it tells us to plot |xp/r| versus w/wn is the r in the |xp/r| the fixed distance or the ratio w/wn?
It's the fixed distance of the eccentricity. I'm going to send an email to the whole class shortly on that problem.
Re: Homework 7, due October 13.
Posted: Tue Oct 13, 2015 1:48 pm
by goodwine
Someone asked me:
I have a question about problem 4.27 part 1. I think I told you that I am using my roommate's book. In his book, he changed the forcing function we are supposed to prove to have a sine instead of a cosine. Do I ignore that change? I would assume so, but I want to make sure.
You can use sine or cosine, it really doesn't matter.