If a straight tunnel is bored from the north pole to the south pole of the earth and if a body is dropped into that tunnel then what time will the body take to move from one and to the other end of the tunnel?

Explanation

`T=2pisqrt(R/g)=2pisqrt((6400x10^3)/9.8)` =1h 24 min 38 sec. time to reach from one end of tunner to another tunnel is `T/2=42` min.