Question

A planet of radius R = 1/10 x (radius of Earth) has the same mass density as Earth. Scientists dig a well of depth R/5 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 x 10⁶ m and the acceleration due to gravity of Earth is 10 ms^-2) 

(A) 96 N 

(B) 108 N 

(C) 120 N 

(D) 150 N

Answer 1

Correct option is (B) 108 N 

Inside planet

Force to keep the wire at rest (F) 

= weight of wire

Also, R = R_e/10 ; putting all values, F = 108 N