1.a piston cylinder device whose piston is resting on top of a set of stops initially contains 0.5 kg of helium gas at 100kpa and 25 degree C.the mass of the piston is such that 500kpa of pressure is req to raise it.how much heat must be transferred to the heliu  b4 the piston starts rising?

2.a pressure cooker has the liquid screwed on tight.a small opening with A=5mm^2 is covered with a petcock that can be lifted to let steam escape.how much mass should the petcock have to allow boiling at 120 degree C with an outside atm at 101.3kpa?

 Since the process is isochoric thus 

Here P1 = 100 KPa, T1= 298 K, P2=500 KPa, T2=?

Solving T2= 1490 K

Also n -> no. of moles of helium = 500/4 =125 

C_v-> sp. heat at constant volume for monoatomic gas is 3/2 R

Thus heat required is Q= nC_v(T2 - T1)

= 125 * 1.5* R * 1192

= Calculate to get your answer. ( R is gas constant )

All the best keep solving and asking.

Mustafa Sir.