1 Lab #5 – Conservation of Mechanical Energy PHY 101 Intro to Physics Glendale Community College © 2019 Glendale Community College 5 – 1 Name Experiment 5 Conservation of Mechanical Energy Objective...

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1 Lab #5 – Conservation of Mechanical Energy PHY 101 Intro to Physics Glendale Community College © 2019 Glendale Community College 5 – 1 Name Experiment 5 Conservation of Mechanical Energy Objective Test the law of conservation of total mechanical energy and to use the projectile velocity resulting from that analysis to predict the horizontal range of the projectile. Equipment Spring gun, projectile (steel ball), 1 and 2 meter sticks, white paper, carbon paper, lab stands, finger clamps and tape measures. Procedure Part 1: conservation of energy Set up the apparatus as demonstrated. Make sure the zero end of the 2.0 meter stick is even with the center of the ball when the ball is at the position where it will leave the spring gun, not the ball position when the gun is loaded. Test shoot the ball and determine where to place the stand so that you can read the position of the maximum height the ball attains. Shoot the ball straight upward five times and record the position of the ball at its highest point each time. You might do something clever with your phone to record the maximum height of each shot. After the first shot, show your instructor the first height value to make sure you are recording the heights accurately. Record the heights to the nearest mm in Table 1. Table 1. Maximum Heights h1 (m) h2 (m) h3 (m) h4 (m) h5 (m) Average h (m) Calculation of ball velocity Using the law of conservation of mechanical energy, we obtain ½ mp V 2 = mp g h, (1) Where h is the average height from Table 1, mp = ball (projectile) mass, g = acceleration due to gravity (9.8 m/s 2 ) and V = the speed the ball leaves the gun. Clearly, we can drop mp from equation 1. Rearranging and solving equation 1 for V gives: (2) Lab #5 – Conservation of Mechanical Energy PHY 101 Intro to Physics Glendale Community College © 2019 Glendale Community College 5 – 2 Use equation 2 to calculate V. V = m/s. Part 2: projectile motion and prediction based on your result from part 1.  Set the spring gun horizontally on a bench near the edge of a bench so that the ball will fly horizontally off the bench when shot. Make sure the ball is hanging over the edge of the bench. You should probably clamp the gun to the bench.  Determine a point on the floor directly below the release point of the ball and mark this point. You may put some masking tape on the floor and make a mark on it.  Measure the height from this point to the bottom of the ball. H = m Predict how far the ball will travel horizontally when shot horizontally from a bench. You will use the same equation derived in the free fall experiment, but this time you will solve for time. Solving for time gives , (3) where g = 9.8 m/s 2 and t is the amount of time the ball is in the air. Calculate the time using H and equation 3. t = s. Show the time you calculate to your instructor to make sure it appears reasonable. D = V t (4) Use equation 4 and the values of V and t to calculate D. D is the predicted distance. D = m  Test fire the ball a couple times to get an idea where it will land  Tape a few sheets of white paper (and carbon paper upside down on the white paper if available) on the floor in the area where the ball landed. Make the paper target wide to allow for side to side inaccuracy in the gun.  Shoot the ball 3 times and using the tape measure, measure the distance from the point directly below the ball (mark on masking tape) to the impact points of the ball on the floor. Record in Table 2. Table 2. Horizontal Distances Distance 1 (m) Distance 2 (m) Distance 3 (m) Average Distance (m) Lab #5 – Conservation of Mechanical Energy PHY 101 Intro to Physics Glendale Community College © 2019 Glendale Community College 5 – 3 Calculate a % difference between the average distance from Table 2 and your predicted distance. Record the values in Table 3. (5) Table 3. Distance Comparisons Predicted D (m) Average D (m) % difference Analysis and Questions 1. Perform the algebra to turn equation 1 into equation 2. 2. Use equation 2 from lab 2 and derive equation 3. 3. Look at your results in Table 3. Is the concept of conservation of energy supported by your results? Consider the %difference… Please explain, don’t just say yes or no. 4. What real force exists during the performance of the experiment that could affect h or D and is not accounted for in the equations?