Searching through old experimental equipment a physics student found a parallel plate capacitor. Being a young physicist he immediately had the strong wish to test it out. He measured the distance between the capacitor’s plates to be d and next he charged the capacitor to the voltage U. Now the student placed a ball between the capacitor’s plates. The ball dropped down on to the bottom plate and then started to rise up again. The time it took the ball to rise from the bottom plate to the upper one was t. Find the ratio of the ball’s mass and the charge received from the bottom plate.