## 5 thoughts on “3.27”

1. codychalmers says:

in part a you had (Mr)/(Mr+Mp) but in part c you had (Mp)/(Mr+Mp) why did it change?

1. tutorpaul says:

I think I just mis-wrote it while I was recording, the numbers should reflect using $\frac{M_R}{M_R+M_P}$ throughout the problem.

2. maeenswileh says:

howdy
First, thanks for the tremendous help.
For this question I think you got the first and the second part wrong, I couldn't find why for the first part, but for the second part you changed the dumping and I think this what changed the final answer the right answer is 0.915 mm which is in the back of the book. part b asked you to change the stiffness only and leave the damping and mass without change.
Thanks again for the help

1. tutorpaul says:

I think your interpretation of the second part is wrong. In my reading of it the dashpot (i.e. the piece of hardware providing the damping) is kept the same while the spring (the hardware providing the stiffness) is changed. What this means is that the coefficient of damping $c_{eq}$ is unchanged while $k_{eq}$ is reduced by half; here we must remember that $\zeta$ (the damping ratio)is not the same as $c_{eq}$; $\zeta$ is influenced by the mass and stiffness just as much as by the damping.