Thermodynamics- 1st Law Question

FordRanger4x4

1. The problem statement, all variables and given/known data

A gas is enclosed in a container fitted with a piston of cross-sectional area 0.1 m2. The pressure of the gas is maintained constant at 8 kPa, while the gas is heated slowly and the piston moves outward a distance of 40 mm. Heat input to the gas during this process is 42 J. What is the increase in internal energy of the gas?

2. Relevant equations

I know that the first law needs to be used here, and i am neglecting Kinetic and Potential Energy

Q-W=(delta)U

3. The attempt at a solution

Im having trouble solving for work, this is what i have so far.

42J-8KPa(V2-V1)=(delta) U

any help would be great, thanks

FordRanger

p21bass

You don't really need to know V1 and V2. You only need the change in volume. Since you have the cross sectional area of the cylinder and the displacement, you can find delta-V and complete your problem.

FordRanger4x4

Thanks, i ended up figuring it out pretty soon after posting.