Here is my problem. A vertical cylinder of cross-sectional area .04m^2 if fitted with a frictionless piston with a mass of 13kg. Assume acceleration of gravity is 9.8 m/s^2. If there is 1 mol of an ideal gas in the cylinder at 315 K, find the pressure in the cylinder. Assume the system is in equilibrium. Here is what I've been doing. P=Force/Area Force= Pressue * Area Since it is in equilibrium, the downward force of the piston should equal the upward force of the gas. PA = (Piston mass)(gravity) P(.04) = (13)(9.8) P = 3185 Pa 3185 is not the right answer according to my online answer checker. What am I doing wrong?