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(A)persuming thaat the arrows in the figure below represent equal force ,what is the...

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quddoos | (Level 1) Valedictorian

Posted September 8, 2013 at 11:23 AM via web

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(A)persuming thaat the arrows in the figure below represent equal force ,what is the net force on the pencil?what motion will the pencil expercince as a reult? 

(B)persuming that the arroes in the figure below are represent equal forces ,what is net force on pencil B ?what motion will the pencil experince as a result ?

(hint)for question (A)  the arrows are in the middle of the pencil from upside and downside ?(B)the one arrows is at the edge of the pencil and the other arrow is near the point of the pencil?   sorry i cant draw the daigram of the pencil.

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shaunak2013 | Student, Graduate | (Level 2) Adjunct Educator

Posted October 6, 2013 at 12:24 PM (Answer #1)

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(A) - look, then, as Newton's third law states, the equal and opposite motions cancel each other out. Plus, they act at almost the same point, so their moments( Moment of Force = Force X Radius of action) will be the same as well. In both cases, Radius of action (r) = l/2 (l is length of pencil).

So, M1-M2 = F1Xr1 - F2Xr2 = F(r1-r2) = 0.

Net force, is clearly, = 0. The pencil will experience no motion at all.

(B) Now, since you did not mention the points of their action, I can only assume that they're acting at exactly the end points of the pencil.

They will thus, produce a couple. The moment of that couple = (F2-F1) x l. (l  = length of pencil).

NO FORCE will act on the pencil, but a rotational motion will act, hence the pencil will move in a clockwise or anti-clockwise direction, depending on the nature of the forces mentioned.

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