2. A family uses several planks to slide a 350 kg crate onto the back of a pickup truck. The box of the pickup is 81 cm above the ground and the planks are 3.0 m long. An average force of 1500 N is required to slide the crate up the planks. (3) a) Determine the work done in loading the crate. b) Calculate the efficiency of the planks as a simple machine to load the crate. c) Where does the rest of the energy go?