Thermodynamics of heating water in a cylinder with piston

[yy205001]

Homework Statement

Consider water contained in a cylinder at 25C with a frictionless piston with some weights on it. Initially the pressure inside the piston is 100kPa and then the water is heated such that the water does 290kJ/kg of work on the piston. Find the final temperature of the water.

Homework Equations

First Law: E_in-E_out=ΔE_system

The Attempt at a Solution

Since heat is added and work in done by the system, by the first law,
q_in-w_out=Δe_system=Δu=c_v(T₂-T₁)

q-290=c_v(T₂-T₁)

But how can I get q in order to calculate T₂?

Thank you

 

[BvU]

You will need more equations than just the one under 2.
c_v requires v constant. How can the water do work if the piston doesn't move ?

 

[yy205001]

Can I assume the pressure is constant during the process?

 

[haruspex]

Can I assume the pressure is constant during the process?

Why would the pressure change? What determines the pressure in this set-up?

 

[yy205001]

The pressure is 100kPa in state1 but did not mention about the pressure about state2?

 

[DEvens]

What would "a frictionless piston with some weights on it" mean about the pressure before and after?

 

[Chestermiller]

How can the pressure on the water be 100 kPa if the piston has weights on it? Isn't that just atmospheric pressure? Or is the 100 kPa gage pressure?

Chet