Me: Entropy, Enthalpy, Polytropic, Adiabatic, Carnot Cycle, Re-heat Regen Cycle, Gas Turnine - Steam cogen.. Easy! Deflection, Kinematics, Vibration Tri-Axialllalalal Stressss what??? lol
MD&M practice problem of the week
- Thread starter Slay the P.E.
- Start date
Help Support Professional Engineer & PE Exam Forum:
I really enjoyed all of the Thermo (Heat Transfer, Thermal Fluid, etc.) classes in college. But i just don't delve into those subjects much anymore for work, so i'd be wayyyy out of practice. I wouldn't mind refreshing on that stuff again, but studying for the MDM (a bazillion topics) is already enough for this year.
Lol I actually did better in thermo and heat transfer than statics and dynamics in school. Using machine design stuff at work over the last 6 years helped keep the basics relatively fresh in my head and made studying easier.
On another note, finally got my license number today
great start to a vacation week.
On another note, finally got my license number today
great start to a vacation week.
Slay the P.E.
Well-known member
Brand new practice problem of the week:
Platform P is supported by four springs, each having a stiffness of 55 pounds-force per foot and has a load rigidly attached to it. The load and platform have a combined mass of 44 pounds-mass. The floor is subjected to a vertical displacement with amplitude 0.4 inches and a frequency of 1.27 Hertz. Under these conditions, the amplitude (inches) of the steady state vibration is most nearly:
(A) 0.40
(B) 0.66
(C) 0.86
(D) 1.04
Platform P is supported by four springs, each having a stiffness of 55 pounds-force per foot and has a load rigidly attached to it. The load and platform have a combined mass of 44 pounds-mass. The floor is subjected to a vertical displacement with amplitude 0.4 inches and a frequency of 1.27 Hertz. Under these conditions, the amplitude (inches) of the steady state vibration is most nearly:
(A) 0.40
(B) 0.66
(C) 0.86
(D) 1.04
MikeGlass1969
Well-known member
OOF!!! I can not remember how to approach these problems... Partial Credit Given?
Slay the P.E.
Well-known member
Slay the P.E.
Well-known member
(B) is correct, but it would be nice if you showed more of your work for the benefit of other readers
Maybe upload a picture or scanned PDF?
Wow, now we have to show our work!?!?! Hard chargers around here! Give me a couple of minutes and i'll see if i can get the solution uploaded.
View attachment Support Vibration.pdf
View attachment Support Vibration.pdf
Last edited by a moderator:
Slay the P.E.
Well-known member
Beautiful.
One observation: The spring constant is given in pounds-force per foot. The mass of the system was given in pounds-mass. Therefore, the calculation of the natural frequency is sqrt[ (18.33lbf/in) / (44lbm) ]
From your work it appears you thought the 44 were pounds-force (a weight) because you replaced "m" with "W/g" and used W=44lb. It turns out to numerically be the same. I'm just worried that you're using the symbol "lb" for "lbf" and also for "lbm".
MikeGlass1969
Well-known member
Slay the P.E.
Well-known member
I am getting 2.5...can you someone help to how to do? Calculate the Euler stress and compare with Sy/2?
