Physics 104 Conservation of Energy (CE) Lab

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Milo Washington
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1 Physics 104 Conservation of Energy (CE) Lab In this activity you will investigate the conservation of mechanical energy as the gravitational potential energy of a falling weight is converted into kinetic energy of the falling weight and a moving cart. If an object of mass M is moving with velocity v, the kinetic energy (KE) associated with the objects motion is KE = 1 2 Mv2. If the object moves a vertical distance h, it either gains or loses an amount of gravitational potential energy (GPE) given by GPE = Mgh, Where g = 9.8 m/s 2 is the acceleration caused by gravity. The object gains GPE if it moves upward and loses GPE if it moves downward. Remember that the right hand sides of both the equations above are general definitions. They have to be properly setup for the particular experiment. We will do this below for you. Procedure TASK 1: Start the program Start the Data Studio program and configure it to use the photogate to measure the velocity of the cart. TASK 2: Experimental Setup Look at the diagram shown in the next page, which should be quite familiar to you. Energy is a concept designed to account for the effects of forces on the state of motion of an object. Its most powerful application, however, is contained in the principle known as the Law of Conservation of Energy. We will test this law with the help of the setup. The law of conservation of energy for this setup is GPE lost by falling weight = KE gained by rolling cart + KE of falling weight (M holder + M brass weights ) g X = 1/2 (M cart + M picket fence + M holder + M brass weights )v 2 (1) 1

2 Ini t ia l Fin a l x x TASK 3: Measuring Mass. a) Find the mass of the cart. Convert the value in kilograms and put that in cell B2 of table CE.1 b) Now add all the mass in column B and put the total in cell B5 of table CE.1. This is the total Mass of the cart M A that you will use in your calculations. c) The weight of the hanger + 50 g mass is already given to you as M B. TASK 4: Take the data a) Place a 50 g weight hanger, which should be hanging on the end of the string that passes through the pulley and hangs over the side of the lab bench. b) Choose a reference mark (V) on the cart on the side of the cart. c) Slowly pull the cart 10 cm back to the left of the photogate and start the program to measure the data. Release the cart. d) Record the data in cell B2 of table CE.2 provided to you in your CE worksheet. e) Repeat b), c), and d) four more times and record all five values in cell B3 through B6 and their average in cell B7 of the table CE.2 below. f) Now pull the cart back 20 cm to the left of the photogate and start the program to measure the data. Release cart. Record the value in cell E2 of table CE.2. g) Then repeat step f) four more times and put the data in cells E3 through E6 and put the average in cell E7. TASK 5: Analyze the data Calculate the required information (see? mark) in table CE.3a and CE.3b provided to you in your CE worksheet. Note that values of M A and M B = kg come from table CE.1 2

3 and V 1 and V 2 come from table CE.2. Also take note of brackets in the multiplication. Your relative difference should be within 20% in both trials. If not than you are probably doing something wrong in your calculations. Answer the questions that are listed in your worksheet. TASK 6: Data Analysis a) If you were working with a partner, then at this point you can proceed to complete the activity on your own. b) You and your partner should already have the necessary data on hard copy table CE.1, CE.2, CE.3a and CE.3b. c) Turn in your group worksheet when you are finished. 3

4 Conservation of Energy (CE) Worksheet Page 1 of 2 Name: Partner: Partner: Date: CE.1: A B C D E 1 Item Mass in kg Item Mass in kg 2 Cart Hanger Picket fence Total M A Total M B CE.2: A B C D E 1 (X=0.10 m) Velocity in m/s (X=0.20 m) Velocity in m/s 2 First trial First trial 3 Second trail Second trail 4 Third trial Third trial 5 Fourth trial Fourth trial 6 Fifth trial Fifth trial 7 Average velocity for 5 trials V 1 Average velocity for 5 trials V 2 CE.3a: (X=0.10 m) GPE = (M B ) (9.8) (0.10) Joules KE= (0.5)(M A + M B ) (V 1 2 ) Joules Re lative difference (in %) = GPE KE GPE 100 4

5 CE.3b: (X=0.20 m) GPE = (M B ) (9.8) (0.20) Joules Conservation of Energy (CE) Worksheet Page 2 of 2 KE= (0.5) (M A + M B ) (V 2 2 ) Joules Re lative difference (in %) = GPE KE GPE 100 Questions for Task 5: Analyze the data 1. In both trials what happen to the magnitude of kinetic energy as the cart rolls on the track? 2. In both trials what happens to the magnitude of gravitational potential energy as the hanging mass falls? 3. In both trials is the relative error less than 5%. If your answer is no, explain why you have a larger error. If your answer is yes under, what condition can you say that the law of conservation of energy is valid? 5

LAB 3: WORK AND ENERGY

1 Name Date Lab Day/Time Partner(s) Lab TA (CORRECTED /4/05) OBJECTIVES LAB 3: WORK AND ENERGY To understand the concept of work in physics as an extension of the intuitive understanding of effort. To