Math Is Fun Forum

GurraTedden

Member

Registered: 2005-07-20

Posts: 19

Mechanics problem

Uhum, I was just hoping that there's someone knowing something about
mechanics, or just can flick an eye on my calculations for this problem.
MathIsFun and mathysperson I'm sure will recognize one of these two problems.

http://engman.bravehost.com/mechanics/2probs.JPG

On 7.14 you can have a look of how far I've got, but I'm stuck.
http://engman.bravehost.com/mechanics/incomplete_solution714.JPG

7.39 I haven't a clue how to do it. The answer is: angle between 32.8 and 45 degrees. The 45 degrees
seems logic, and I guess that should calculate the intuition way. I'll buy that.

IF this is the wrong forum, if you wanna strictly do math around here, I would really appreciate a similar
forum with mechanics.

/Mr. G

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Mechanics problem

Hi Gustav,

I have had a brief look at the first problem, and understand it enough to know that I need to sit down quietly with a pad and paper to solve it. Can it wait a day?

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

GurraTedden

Member

Registered: 2005-07-20

Posts: 19

Re: Mechanics problem

Of course. I'm just happy that you give it a try.

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Mechanics problem

OK, you should be able to solve the bar on its own, then proceed to solve the cylinder later

How about another moment formula?

∑Mb = 1.0(Fa cosθ - Na sinθ) - 0.25 mg cosθ 

(better check I have that oriented correctly)

Then you have three equations and three unknowns:

∑Fx = Fa - Nb sinθ + Fb cosθ
∑Fy = Na - mg + Fb sinθ + Nb cosθ
∑Mb = 1.0(Fa cosθ - Na sinθ) - 0.25 mg cosθ

(known: Nb=141.1, mg=24 x 9.81, sinθ=0.6, cosθ=0.8)

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

GurraTedden

Member

Registered: 2005-07-20

Posts: 19

Re: Mechanics problem

OK! THIS IS ALL SOLVED NOW! No more problems!