3. A certain amonut of gas molecules are sealed in a container (see the picture below), the top of the container is a movable and frictionless piston. The space above the piston is vacuum. Initially there is a weight on the piston to hold the position of the piston (left). Suddenly the weight disappears (middle) and the piston pushes up quickly (right). During the process, what is the work done on the system? Can you use -pdV, where p is the pressure of the system, to calculate W during the process? If not, why? piston vacuum vacuum