How to determine maximum deflection

H

Hamzahussein

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Nov 19, 2020
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Can someone show me how to do this type of question? Or link to some worked example or something? I try to find dy/dx to get maximum value but it didn’t work.

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Can we see your work so we can point out your error? What did not workout after you found dy/dx? Post back with your work.
 
Well I got the right answer in the end by assuming dy/dx =0 at x=L/2. Then I substitute L/2 in the original equation. But I don’t get how to differentiate the original expression. Like which rule to use etc.
 
I'm confused. How did you set dy/dx equal to 0 if you don't know how to find dy/dx.

Can you find the derivative of 7(3x^3 + 5x^2 -7x)? What is the difference, if any, between the problem I just gave you and you finding dy/dx for your problem?
 
Jomo said:
I'm confused. How did you set dy/dx equal to 0 if you don't know how to find dy/dx.

Can you find the derivative of 7(3x^3 + 5x^2 -7x)? What is the difference, if any, between the problem I just gave you and you finding dy/dx for your problem?
Click to expand...
S/he used symmetry to invoke dy/dx =0 at the point of symmetry!
 
Hamzahussein said:
Well I got the right answer in the end by assuming dy/dx =0 at x=L/2. Then I substitute L/2 in the original equation. But I don’t get how to differentiate the original expression. Like which rule to use etc.
Click to expand...
Are you saying that - you don't see this differentiation as simple use of "power law of differentiation"?

\(\displaystyle \frac{d}{dx}x^n \ = \ \frac{x^{n-1}}{n} \ \ \ for \ n \ \ne\ -1 \)
 
Subhotosh Khan said:
S/he used symmetry to invoke dy/dx =0 at the point of symmetry!
Click to expand...
Yes, the question states that the beam is uniformly loaded So I assumed the max deflection was in the center.

I have tried using the power law and I got to

(w/12EI)(x(2x^2 - 3Lx +L^2))

but not sure where to go from here, I don’t know how to factor the quadratic with the extra terms L and L^2, or what to do with it after that. This is my first time dealing with a problem like this.
 
Hamzahussein said:
Well I got the right answer in the end by assuming dy/dx =0 at x=L/2. Then I substitute L/2 in the original equation. But I don’t get how to differentiate the original expression. Like which rule to use etc.
Click to expand...
What do you need to FIND?
 
Thanks for the replies, I don’t know how to factor a quadratic that looks like that. This is the part I have trouble with, I normally use quadratic formula but I don’t know what to do with L and L^2.
 
Can you find the derivative of (3x^3 + 5x^2 -7x) and post back with your work? How about the derivative of 7(3x^3 + 5x^2 -7x)? Finally how would you compute the derivative of A(Bx^4 + Cx^3 + Dx^2)???
 
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