Q.

A metal wire of uniform mass density having length L and mass M is bent to form a semicircular arc, and a particle of mass m is placed at the centre of the arc. The gravitational force on the particle by the wire is _____.  [2024]

1 0  
2 GMmπ2L2  
3 2GMmπL2   
4 GMmπL2  

Ans.

(3)

Eg=2·G·λR=2GML·R

also, πR=L    R=Lπ

  Eg=2GML·Lπ=2GMπL2

F=mEg=2GMmπL2