Momentum ~ Lab Name:

Transcription

1 Momentum ~ Lab Name: Instructions: Using a pencil, answer the following questions. The lab is marked, based on effort, completeness, neatness, and accuracy. Do your best! Part 1: Explosion In this section, you will be referring to the Lab Resources > Video & PDF: Cart Explosion 1. What does the slope of a d vs t graph show? 2. Where, on a d vs t graph, should the slope be measured if you were looking to measure the velocity of an object immediately after an explosion? Describe and/or sketch. 3. Note that sometimes graphs don't distinguish direction in the way they are plotted. In these cases, you decide which direction is the positive direction and include it with the velocity. If two objects moved in opposite directions, what could you say about their respective velocities and momentums? 4. Show your calculation for the velocity of Cart #1 after EXPLOSION #1 (remember sign [per 5. Show your calculation for the velocity of Cart #2 after EXPLOSION #1 (remember sign [per 6. Show your calculation for the velocity of Cart #1 after EXPLOSION #2 (remember sign [per 7. Show your calculation for the velocity of Cart #2 after EXPLOSION #2 (remember sign [per Page 1 of 5

2 8. Using the velocity calculations from the previous page, complete the table below. Remember your signs and units. Explosion #1 Cart #1 Cart #2 Total Momentum mass 500 g 500 g xxx V i zero zero xxx V f xxx p i zero zero zero p f Explosion #2 Cart #1 Cart #2 Total Momentum mass 500 g 1000 g xxx V i zero zero xxx V f xxx p i zero zero zero p f 9. Given the initial Total Momentum, what should be the total Final Momentum close to? Why? Page 2 of 5

3 10. Based on your observations and analysis of the lab, what was the experimental difference between the total initial and final momentum for each explosion. Because both carts are not moving before the plunger is released, we need to compare the momenta of the two carts after the explosion. To avoid having to divide by zero, use the following formula (the bars represent absolute value): Momentum of Cart1 Momentum of Cart 2 % difference = x 100 Momentum of Cart1 Explosion #1 Explosion #2 11. Consider the % differences you calculated above. Given that every lab will result in a bit of lab error, but should be "within reason" if you designed a good lab, does your % differences seem reasonable? What might be a few sources of error? 12. Before something explodes, it is often not moving. After the explosion, though, its pieces are moving in all directions with varying speeds. How can it be said that the net momentum after the explosion is zero? Draw a vector diagram to explain. Page 3 of 5

4 Part 2: Collision In this section, you will be referring to the Lab Resources > Media: Collision Lab. 1. In the green box on the right side of the screen, select the following settings: 1 dimension, velocity vectors ON, momentum vectors ON, reflecting borders ON, momenta diagram ON, elasticity 0%. Look at the red and green balls on the screen and the vectors that represent their motion. a. Which ball has the greater velocity? b. Which has the greater momentum? 2. Explain why the green ball has more momentum but less velocity than the red ball (HINT: what is the definition of momentum?). 3. Push play and let the balls collide. After they collide and you see the vectors change, click pause. Click rewind and watch the momenta box during the collision. Watch it more than once if needed by using play, rewind, and pause. Zoom in on the vectors in the momenta box with the control on the right of the box to make it easier to see if necessary. 4. Change the mass of the red ball to match that of the green ball. a. Which ball has greater momentum now? b. How has the total momentum changed? c. Predict what will happen to the motion of the balls after they collide. Page 4 of 5

5 5. Watch the simulation, and then pause it once the vectors have changed. 6. Now change the elasticity to 100%. Predict the motion of the balls after the collision. 7. Watch the simulation, and then pause it once the vectors have changed. Page 5 of 5