Hello my name is Chris I go to NJIT and my professor gave a problem to solve and I am baffled. I thought I had it but, he said no. Any help is greatly appreciated this is very important for my grade. Thank you.

The Question:

There is a tunnel spanning from NY to LA. There is a Train in the tunnel and he wants the time it takes to reach the end and also the velocity it has.

In the picture below i tried to illustrate it. X=5400km and r=6400km.

This is my work i got the equation T = π √ (R/g) from another equation with force+massdensityofearth x G x X x pi x m=0

He gives a multiple choice like answer key

velocity is either:

6000m/s

600m/s

60m/s

6m/s

0m/s