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JEE Advanced · Physics · 9. Gravitation

A planet of radius R=110× (radius of Earth) has the same mass density as Earth. Scientists dig a well of depth R5 on it and lower a wire of the same length and of linear mass density 10-3 kgm-1 into it. If the wire is not touching anywhere, the force applied at the top of the wire by a person holding it in place is (take the radius of Earth =6×106 m and the acceleration due to gravity of Earth is 10 ms-2 )

  1. A 96 N
  2. B 108 N
  3. C 120 N
  4. D 150 N
Verified Solution

Answer & Solution

Correct Answer

(B) 108 N

Step-by-step Solution

Detailed explanation

Inside planet
gi=gsrR=43Gπrρ
Force to keep the wire at rest (F)
= weight of wire
=4R5Rλdr43Gπrρ=43Gπρ9λ50R2
Here, ρ= density of earth =Me43πRe2
Also, R=Re10 ; putting all values, F=108 N
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