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Two separate wires A and B are stretched by 2 mm and 4 mm respectively, when they are subjected to a force of 2 N. Assume that both the wires are made up of the same material and the radius of wire B is 4 times that of the radius of wire A. The lengths of the wires A and B are in the ratio of a:b. Then a/b can be expressed as 1/x, where x is ______.

Asked in JEE Main 18th March 1st Shift 2021 · Elongation under a load

Answer: 32

Step-by-step solution

Given: the same material and the same force F=2 N, with r_B=4r_A.

Δ l=(FL)/(π r²Y), so L=(π r²Y Δ l)/F and L∝ r²Δ l.

(L_A)/(L_B)=((r_A)/(r_B))²×(Δ l_A)/(Δ l_B)=1/(16)×2/4.

(L_A)/(L_B)=1/(32).

Hence x=32.

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