31. 1. Use the graph below to find the work done. Show your calculations. Force Ep = Ep + Ex (N) 10+ S. 10 Position (m) 2. What is the Work/Energy Principle and how can it be applied to problem solving? Ep = mgh 3. What are the units of work and how do they compare to the units of energy? EX = 1 / , mv 2 4. Describe the energy transitions that take place when a person draws back a bow with an arrow and then shoots the arrow at a target. The arrow stops when it imbeds in the target. Ee = 1 /2 Kx 2 Solve the following problems demonstrating good technique: show your work, include correct sig. figs. and units, and be neat and thorough. 5. An object is shot straight up into the air with a total Ex of 240 J. How much potential energy does it have when it reaches its peak height? What is the Ep and Ex when it is half way up on its path? W = AE 6. A 220 kg piano needs to be lifted by an electric motor a total of 35 m. If the motor has a rating of 1250 W, how long (time) will it take to lift the piano? W = Fd 7. How high can a 15.6 kg object be lifted against gravity if there are a total of 1500 J of energy available? (Is this a work problem or a potential energy problem?) P = wHooke's Law and Elastic Potential Energy Look for conversions * F = -kx Ex = /2K x 2 x = clisplacementc Show your work Fw= mg K = Spring constant 1. What is the elastic force a spring will exert if it has k =165N/m and is stretched 0.44m? 8/m 2. How far must a spring (spring constant= 44N/m) be pulled in order to exert a force of 76N? 3. How long will a spring with rest length 82.0 cm and spring constant 0.600N/m be if it is stretched until it exerts 0.250N? 4. A spring has a rest length of 1.20m. When a 22kg mass is hung on it, it stretches to 3.60m. What is its spring constant? 5. What is the elastic potential energy of a bow with spring constant 150N/m if it is pulled back 42 cm? ET = 1 / 2 K x 2 X = 42 cm F 2 ( 150 N ) ( 42 ) 2 K= 150 N/ m EE = 12600