Hi folks,
This week we discussed the concept of impulse and how it relates to momentum. To investigate this further, we shot spitballs to illustrate how the time of the force affects momentum.
We also did the famous egg drop experiment where the students had to design a vehicle that kept a raw egg safe from a 15 foot drop. There were some brilliant designs!
For homework this week:
1. In your own words, describe to me what shooting spitballs has to do with impulse?
2. Use the concept of impulse to explain why it's so important to follow through when doing some sort of a sporting activity.
3. During the egg drop activity, you used several strategies to try to keep your egg from breaking. List three of those strategies and tell me what they had to do with impulse and momentum.
Also, Do the following questions. (Answers below.)
1. A Denver Bronco is running towards the end zone at 11 m/s (25mph). A Pittsburg Steeler running directly behind him at 15 m/s (34mph) tackles him and causes him to fumble directly into the hands of another Steeler who runs it back for, the final seconds, game winning touchdown!!! If the Bronco weighs 127 kg (280lbs) and the Steeler weighs 136 kg (300 lbs), what is their velocity after impact and before hitting the ground? (Use metric #'s only. Others are there for reference.) (Check answer when finished below.)
2. Two train cars are moving towards each other along a track. One has a mass of 32,000 kg and is traveling at 3.5 m/s. The other has a mass of 23,000 kg and is traveling at 5 m/s. Assuming they stick together after impact, what is their final velocity? (Check answer when finished below.)
3. Describe throwing a bowling ball down the alley and knocking down all the pins as far as momentum transfer goes. Start with holding the ball and end with the last pin falling. Extra Credit: Show me the #'s and calculations.
AND
Use this websitehttp://phet.colorado.edu/sims/collision-lab/collision-lab_en.html to complete the following questions:
Please let me know if this website doesn't work for folks. It works fine for me but I'm not sure it will work for all of you.
Phet Momentum Homework
1. Click on the Advanced tab at the top of the window.
2. Click on "One Dimension" in the box to the upper right.
3. Click on the "Momenta Diagram" button in the upper right.
4. Click on the "Show Values" button in the upper right.
5. Set the speed of ball 2 to 0 (Drag the vector arrow for ball 2 until V = 0)
6. Notice the total momentum of both balls. (In the momenta box to the lower right)
7. Click play.
(Be sure you look at the numbers for the following questions before either ball bounces off the wall. If you wish, you can turn off "Reflecting Border" in the upper right corner.
8. How does the total momentum of the system after collision, compare to the total momentum before collision?
9. Now, make both balls have a mass of 1.5. What happens to their velocity after collision?
10. How about their total momentum before and after collision how do they compare?
11. Now click "Add Ball" at the bottom. This ball should have a mass of 2 and a velocity of 0. What is the total momentum?
12 Now click play, what is the total momentum after collision?
13. Click on the "Momenta Vectors" button in the bottom right.
14. Click on remove ball so that you only have 2 on the screen.
15. Notice the momentum vectors. Look carefully at the total momentum vector.
16. Click play. After collision how does the total momentum vector change?
17. Add a ball and do it again. Notice anything about the momentum vector now?
18. Please feel free to play with this. Add balls, try two dimensions, what ever you wish.
Answers to math problems.
1. MV of Bronco + MV of Steeler = Mass of both x velocity of both
(11m/s x 127Kg) +(15m/s x 136Kg) = 263 x Vf
1397 + 2040 =263v
13.1m/s = V
2. MV of car 1 + MV of car 2 = Mass of both x velocity of both
(32,000 x 3.5) + (23,000 x -5) = 55,000 x Vf (Notice that the second speed is negative due to the opposite direction of travel. I assigned moving right as positive and moving left as negative.)
112,000 + -115000 = 55,000 Vf
-3000 = 55,000 Vf
-.06 m/s = Vf (The cars will be moving slightly to the left after impact.
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