Q$3$: A piston$-$cylinder device is filled with He gas. The mass of the piston and the weight together is $75kg.$ The acceleration of gravity is $9\mathrm{.}81\frac{m}{s^2}$ and the atmospheric pressure is $1\mathrm{.}01325$ bar. If we assumed a frictionless piston. Determine:

a$)$ The force excreted by the atmosphere, the piston, and the weight on the gas if the piston is $80mm$ in diameter.

b$)$ The pressure of the gas.

c$)$ If the gas is allowed to expand by pushing up the piston and the weight $375mm,$ what is the work done by the gas in $J?$

d$)$ What is the change in potential energy of the piston and the wright after the expansion in part c$)$