The potential energy of a catapult was completely converted into kinetic energy by releasing a small stone with a mass of 20 grams. the velocity of the stone when it reached the target was 15.0 meters/second. what was the value of the kinetic energy of the stone when it reached the target?

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.