# Homework Help: Need help finding spring constant from volume, area, temperature and distance

1. Apr 21, 2012

### defmar

An ideal gas is confined to a cylinder by a massless piston that is attached to an ideal spring. Outside the cylinder is a vacuum. The cross-sectional area of the piston is A = 2.50*10^-3 m^2. The initial pressure, volume, and temperature of the gas are, respectively, P0, V0 = 6.00*10^-4 m^3 and T0 = 273 K, and the spring is initially stretched by an amount x0 = 0.800 m with respect to its unstrained length. The gas is heated, so that its final pressure, volume, and temperature are Pf, Vf and Tf and the spring is stretched by an amount xf = 0.1000 m with respect to its unstrained length. What is the final temperature of the gas?

For the life of me, I cannot find the spring constant k that is needed to solve the rest of the entire problem. I know that KE = (3/2)kT, but I don't know KE either. I'm not given the initial pressure, just the variable. Anyone able to help me find k? I'm lost on how to come up with it.

2. Apr 22, 2012

### Andrew Mason

You can't solve for k or n. But you do not have to find k or n.

Just write the expression for P0 in terms of x0, A, V0, n and T0 and similarly write the expression for Pf . When you solve for Tf you will see that k and n drop out.

AM

3. Apr 22, 2012

### defmar

Thank you.

I'm getting T_f = [T_0*(V_0+A*ΔX)*X_f/A] / [(X_0*V_0)/A] solving :)

4. Apr 22, 2012

### Andrew Mason

What is Δx?

What is your expression for P in terms of k, x and A? What is Pf/P0?

What is Pf/P0 in terms of Tf, T0, Vf and V0?

Work out Tf from that.

AM

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