16. Which of the following statements concerning moments is FALSE? (A) Moments h

Question

16. Which of the following statements concerning moments is FALSE? (A) Moments have primary dimensions of length (or force, such as foot-pounds sometimes to avoid confusion with energy units, pound-feet). (B) The moment will be zero when the line of action of an applied fo center of rotation (that is, the actual or assumed pivot point). rce passes through the (C) Rotation is required for a moment to exist. (D object experiences a moment whenever a force is applied to it (even if it is zero, as when the moment arm length is zero). ) An supported beam with applied loads is shown below as well as the shear and bending diagram associated with the system. What is the approximate maximum bending 17. A simply moment moment and maximum shear? 1800 N 900 N 0.35 m 0.85 m 1800 N 00 N 0.35 m R 1 m A0.65 m 372.5 N -427.5 N 1327.5N 8921 N m 464.6 N-m (A) 340 N-m and 430 N (B) 460 N-m and 900 N (C) 660 N-m and 1330 N (D) 890 N-m and 1370 N

Explanation / Answer

16 (c) and (d)

(c) Rotation is not required, because the section can be rigid. For example, the fixed end of a beam has zero rotation, but it can resist moments, and thus the moment exists.

(d) A lever arm is always needed, if lever arm is zero, then moment is also zero. Similarly if the force is zero, the moment is zero.

17. (d)

As is clear from the diagrams, the maximum moment is 892.1 m-N, and maximum shear is 1372.5 N. And (d) has the nearest values.

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