# Civil Engineering - Strength of Materials - Discussion

### Discussion :: Strength of Materials - Section 1 (Q.No.33)

33.

For a simply supported beam of length L, the bending moment M is described as M = a (x - x3/L2), 0 ≤ x < L; where a is a constant. The shear force will be zero at

 [A]. the supports [B]. x = L/2 [C]. x = L/3 [D]. x = L/3

Explanation:

No answer description available for this question.

 Kashi said: (Sep 24, 2013) Maximum bending moment occurs at zero shear force*. d(M)/dx = 0 (for maximum bending moment). on differentiating above equation you get option C.

 Maneesha said: (Aug 15, 2017) Give me the correct explanation.

 Ebeyehu said: (Aug 21, 2017) The derivation of the moment is always shear having this idea we can derivate and we obtain dm/dx =a (1-3x*x/l*l) say this equation is zero and we will get 1-3x*x/l*l =0 from this x=l/3thepower of half.

 Venkatesh said: (Oct 17, 2017) Shear force is the partial derivative of bending moment so to obtain shear force the given bending moment is differentiated with respect to x and submit the given options so that you should get zero.

 Hussein said: (May 27, 2019) 1-(3x2/l2) = 00. x2=l2/3.

 Anjali said: (Dec 24, 2019) Shear force always zero at maximum bending moment. For max BM,dm/dx =0. So 1-3x^2/l^2 =0. Hence, 1-3x^2=0. x=1/3^1/2.

 Shreyas A said: (Oct 31, 2020) We know that, Rate of change of Bending moment, dM/dx = Shear force. Rate of change of Shear force, dF/dx = Rate of loading. So, they gave B.moment as an equation. To get Shear force then differentiate that wrt x and we will get, dM/dx = a( 1 - 3x^2/l^2). Now to get max shear force, dM/dx = 0. so, a( 1 - 3x^2/l^2) = 0. l^2 = 3x^2. x = l/√2.