In a physical balance working on the principle of moments, when 5 mg weight is placed on the left pan, the beam becomes horizontal. Both the empty pans of the balance are of equal mass. Which of the following statements is correct? (a) Left arm is longer than the right arm (b) Both the arms are of same length (c) Left arm is shorter than the right arm (d) Every object that is weighed using this balance appears lighter than its actual weight.

Answer: (c). Empty pans have equal mass P, yet 5 mg must be added on the left to level the beam, so the arms are unequal. Moments about the fulcrum: (P + 5) lL = P lR Since P + 5 > P, we need lL < lR. So the answer is (c): the left arm is shorter than the right arm.

In a physical balance working on the principle of moments, when 5 mg… | JEE Main 2017 (8 Apr, Shift 1)

Q39JEE Main 2017 · 8 APR · SHIFT 1Medium

Torque, Couple & Equilibrium of Rigid Bodies

In a physical balance working on the principle of moments, when 5 mg weight is placed on the left pan, the beam becomes horizontal. Both the empty pans of the balance are of equal mass. Which of the following statements is correct?

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Answer: (c)

Empty pans have equal mass $P$ , yet 5 mg must be added on the left to level the beam, so the arms are unequal.
Moments about the fulcrum: $(P + 5)\,l_L = P\,l_R$
Since $P + 5 > P$ , we need $l_L < l_R$ .
So the answer is (c): the left arm is shorter than the right arm.

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