MD&M practice problem of the week

[Slay the P.E.]

My answer was also B but the calculated value I got was 0.23...answered in 6:23 min....

But you should get 0.179 — there has to be an error somewhere.

 

[emmajuwa]

But you should get 0.179 — there has to be an error somewhere.

Maybe the calculator

Sent from my SM-N950U1 using Tapatalk

 

[SacMe24]

But you should get 0.179 — there has to be an error somewhere.

Yes.. instead of 49.05N for the friction force I wrote 45.05 when I took the natural log...that did it... I do get 0.179...whew....gotta watch out for these simple mistakes on the exam...thanks !

 

[Slay the P.E.]

Last one before the big day next Friday. Good luck to all!!!!

An external point load of 3 kip is applied at point C on the steel bar shown. The bar is supported by two springs at its ends A and B. Each spring has the same stiffness and is originally un-stretched. You may assume the weight of the bar is negligible, and that Young's modulus is E=29,000 ksi. For the bar, I=12 in^4. The vertical displacement at the point of application of the load shall not exceed 1.51 inches. Under these conditions, the stiffness (kip/ft) of each spring is most nearly:

(A) 15

(B) 20

(C) 25

(D) 30

 

[emmajuwa]

Is this question set up right? Deflections at the ends will be zero. Maybe I'm missing something?

 

[Slay the P.E.]

Is this question set up right? Deflections at the ends will be zero. Maybe I'm missing something?

Deflections at the ends are not zero, because the supports are compression springs which will be shortened upon the application of the load.

But, even if they were zero at the ends... the deflection at the point of application of the load is non-zero and is given as 1.51 inches.

What the problem is asking for is the spring stiffness, k.

 

[MikeGlass1969]

I come up with (A)..  15kip/ft

Found the deflection of the beam at the point load.  Then subtracted the deflection from the total deflection.  Created a slope intercept form equation for the slope of the beam due to the uneven deflections of the springs.   

 

[Kloeb222]

I get A as well. Took me a bit too long though. about 12 min because I didn't have any beam tables readily accessible (at work) and had to search through my bookmarked resources online

Same way as Mikeglass describes above.

 

[TWeatherford]

I get A as well.  Maybe it's just me, but I found it to be a challenging problem, but a good one.

 

[Slay the P.E.]

A is the correct answer for the beam deflection problem. Use the principle of superposition to add the displacement of the load application point assuming rigid supports with an elastic beam plus the displacement of the load application point assuming a rigid beam but elastic supports.

 

[emmajuwa]

A is the correct answer for the beam deflection problem. Use the principle of superposition to add the displacement of the load application point assuming rigid supports with an elastic beam plus the displacement of the load application point assuming a rigid beam but elastic supports.

Please do you guys mind sharing your calculation? Thanks.

 

[Kloeb222]

Here ya go. Hopefully this is clear. 

 

[emmajuwa]

Here ya go. Hopefully this is clear. 

View attachment 11035

Thank you so much. i got halfway and got stuck.

 

[Slay the P.E.]

Here ya go. Hopefully this is clear. 

View attachment 11035

You beat me to it. Good work!

 

[Kloeb222]

Is anyone else excited for practice problems of the week to start again? lol 

 

[monty01]

Bring it!

 

[squaretaper LIT AF PE]

Here ya go. Hopefully this is clear. 

View attachment 11035

As a thermal-fluids guy, this makes my stomach hurt. :rotflmao:

 

[monty01]

As a thermal-fluids guy, this makes my stomach hurt. :rotflmao:

Deflection?  Easy!  Now, enthalpy and entropy?  WTH is that all about?!?!?!?  Adiabati-wha????

 

[SacMe24]

Is anyone else excited for practice problems of the week to start again? lol 

I'll probably still look at these just for kicks... :bananalama:

 

[Kloeb222]

Deflection?  Easy!  Now, enthalpy and entropy?  WTH is that all about?!?!?!?  Adiabati-wha????

My thoughts exactly. lol. To each their own..