was 5V - 2.5 = 2.5V then 2.5/0.035=71.43 ohm not the right way to calculate this?
I'm confused about this calculation. Are you trying to make a voltage divider to give less than the supply voltage to the gate?
Mosfets are generally designed to work as basic switches. When they are operated with low gate drive they can be in the "linear region" of operation where the Drain-Source resistance is linearly proportional to the gate drive. They produce more heat when operated this way as their internal resistance is higher than when operated with full gate drive.
If you want to experiment with different gate voltages in your present setup you can simply put a potentiometer in the circuit. One leg to positive rail, other leg to negative rail, wiper to the switch (instead of connecting switch directly to positive rail.) Leave the gate pulldown where it is, on the other side of the switch.
EDIT: I've been back to the post where you introduced this calculation and I can't figure out what you are trying to do. The units of your equation don't even match. You have volts divided by ohms and an answer in ohms -- a unit discrepancy, for one thing.
Mosfets are different than bipolar junction transistors. BJTs require current flowing from Base to Emitter to enable greater current to flow from Collector to Emitter. Mosfets require no such current flow from Gate to Source, rather they require filling the gate "bucket" with charge to turn on and bleeding charge off by the same connection to turn off.
So if you want to supply some reduced voltage to the Gate for some reason, you could use a voltage divider (the potentiometer I mentioned above, or fixed resistors calculated as normal for voltage dividers). And for the output side, you can consider the Drain-Source path through the mosfet as having negligible resistance when Gate "bucket" is full of charge, and more and more resistance as there is less and less charge on the Gate. No gate charge, mosfet is "off" and no current flows between Drain and Source. Full gate charge, mosfet is "ON", fully conducting between Drain and Source.