EXAM 2.4: WORK, ENERGY, POWER PHYS 1208: Electronic sharing of this document or its contents, in whole or part, is prohibited BASIC 3210 N/m 25.2 (1) RNG A very stiff spring (4 - 9000-5000 N/m) is compresssed from its relaxed length by 20-50 cm. Calculate the amount of potential energy stored in the compressed spring. (2) RNG The compressed spring is the launching mechanism of a big cannon. A large watermelon (mass: 12.3 10-20 kg) is loaded into the cannon, and the watermelon is launched horizontally, so that all of the spring's stored potential energy is convered into kinetic energy. Calculate the speed of the launched watermelon. (3) The watermelon is reloaded, then launched straight upward, so that all of the spring's stored clastic potential energy is converted into gravitational potential energy by the time the watermelon reaches its maximum height. Calculate the watermelon's maximum height. (4) RNG During a launch, the spring goes from full compression to complete relaxation in a short time (0 5-0.8 s). Calculate the spring's average power output during a launch. 0.678 The rest of the assignment is about a cable pulling a loaded sled up a smooth icy (friction-free) slope on a windy day. cable wind 56.7 45EN 6: (5) RNG, MVQ The sled's mass is 40-60 kg. the tension in the cable is Fr = 400-700 N, the slope is inclined at 123 2 an angle 6 = 40-30' above horizontal, and the drag force from the wind is Fo = 40-60 N. We're analyzing an interval during which the sled slides d = 10-20 in uphill (d is measured parallel to the slope) Identify all random qtys by description and symbol. = 15.6m FD= 49.IN (6) The slope exerts a normal force Fx on the sled. Explain why Is does no work on the sled during this interval. I sentence. (7) Calculate the work done on the sled by each of the other three forces while it slides d meters uphill: We (work done by gravity), Wr (work done by tension), and Wo (work done by drag). The cable pulling the sled is parallel to the slope, and the drag force is horizontal, in the direction the wind is blowing. (8) At the bottom of the slope, the sled's speed is 6.00 m/'s. Calculate the sled's speed at the top of the slope (after sliding d meters uphill), starting from Was = Ke - K. (9) In #6 you explained why Fx did no work on the sled, but normal forces definitely can do work. Think of a recent concrete example of a time when you used a normal force to do some work, or when a normal force did some work on you. In 1-2 sentences, describe what or who exerted the normal force, what or who it was exerted on, what happened, and whether Fx did positive or negative work
