FarleyPhysics.com

Gravitation Video

Today you will study circular motion.  For this simulation use Firefox if it doesn’t work in Safari.

1. Open the simulation here.

2. Answer the questions on the activity sheet here.  Put all questions (you can shorten them), answers, and draw the diagrams in your notes.  For #8, directly means if you increase one, the other increases.  Inversely means if you increase one, the other decreases.

1. The Science of Snowboarding.

2. Conservation of Energy animations.

3. The Falling Rhino.

4. Examples

5. Problems:

1.  If you drop a 1 kg rock off a building that is 300 m high, what is the rock’s potential energy at the top of the building?  What is the rock’s kinetic energy at the top of the building?

2. What is the rock in #1′s Potential energy half way down the building?  What is the rock’s kinetic energy half way?  What is the rock’s total energy half way?

3. What is the rock in #1′s potential and kinetic energy when it reaches the bottom of the building?  What is it’s total energy?

4. If a 50 kg cliff diver jumps off a 20m cliff, how fast is the diver moving at the top of the dive, at 10 m, and when she hits the water?

5. If a frictionless roller coaster with a mass of 500 kg starts 100 meters high, how fast is it rolling when it is half way down?  How fast is it going when it reaches the bottom?  If it goes up a 25 m hill, how fast will it be going?  If it goes up another hill that rises to 110 m, how high will it go before you have to start lifting it?

6. You throw a 0.2 kg baseball up in the air with a velocity of 20 m/s.  How high will it go?  How fast will it be moving when it reaches half way to the top?  How fast will it be moving when you catch it?

Today you will learn all about the Conservation of energy by studying the motion of a skateboarder. For all the questions below, draw a picture and write the questions and answers.

Run the simulation linked here.  Be sure to click “Run Now”

1. Click the box for Potential Energy Reference. Drag the low point of the skateboard ramp down to the PE=0 line. Draw the ramp and skateboarder in your notes.

2. Slow the simulation down by dragging the sim speed control toward slow and then click the show path button. Why are the dots spread apart at the bottom of the ramp and why are they very close at the top? What do the dots tell you about speed and acceleration? Draw the dots on the drawing from #1 and explain what they mean.

3. Turn on the Energy vs. Position graph, draw it in your notes, then answer the following questions by pausing the simulation at the right time or just watching closely:

3a. What is the total energy when the skateboarder is at the top left of the ramp, the middle, and the top right?
3b. What is the potential energy at the left, middle, and top right?
3c. What is the Kinetic Energy at the top left, middle, and top right?

4. Click Energy vs. Time graph and answer the following questions:
4a. When the kinetic energy is the greatest, what is the potential energy?
4b. When the Potential energy is greatest, what is the kinetic energy?
4c. At any time, what is the total energy?

5. Turn on Track Friction and increase the coefficient of friction a little. Click the Return Skater button on top describe what happens to the skater when friction is present. Is energy conserved when friction is present?

6. Turn on the Energy vs. Time graph and re-run the simulation with friction on. Draw the graph in your notes and label the total, thermal (heat), Potential, and Kinetic Energy. What happens to the potential and kinetic energies? Where does the energy go? Is energy conserved? Why or why not?

7. Add some track to make your skateboarder ride on a roller coaster (loops work!). Draw your track. Drag the skater to the beginning of the track and let him ride. It will work better if you turn friction off.

8. See how your roller coaster works in space by clicking the Location = Space box. Describe what happens.

Potential and Kinetic Energy Problems.
Do these in your notebooks.

1. A 0.2 kg apple in a tree that is 10 m high, has what potential energy?

2. A 0.2 kg apple in a tree that is 5 m high has what potential energy?

3. When the apple in the previous problem hits the ground, what is its potential energy?

4. A 600 kg roller coaster at the top of the highest point on its track which is 50 m, has what potential energy?

5. If the roller coaster in the previous problem went down the track to half of its highest hight, what would its potential energy be?

6. If the roller coaster goes all the way to its lowest point, what is the potential energy of the roller coaster?

7. A 3 kg ball is rolling 2 m/s. How much kinetic energy does it have?

8. Determine the kinetic energy of a 600-kg roller coaster car that is moving with a speed of 20 m/s.

9. If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy?

10. If the roller coaster car in the above problem came to a stop, what would its kinetic energy be?

Tricky Problems

11. Missy Diwater, the former platform diver for the Ringling Brother’s Circus, had a kinetic energy of 12 000 J just prior to hitting the bucket of water. If Missy’s mass is 40 kg, then what is her speed?

12. A 900-kg compact car moving at 60 mi/hr has approximately 320 000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 30 mi/hr.

13. What is the kinetic energy of a 0.2 kg apple that falls from a 10 m high tree? What is the apple’s energy when it is 5 m above the ground?

Go Here and run the simulation.
1. If wagon 1 has a mass of 0.5 and a velocity of 0.2 and Wagon 2 has a mass of 0.5 and a zero velocity, what will the velocity of Wagon 2 be after an elastic collision? What will the velocity be after an inelastic collision?

2. If wagon 2 has twice the mass as it did in #5, what will wagon 2′s final velocity be in an elastic collision? What will the velocity be after an inelastic collision?

3. If the masses of both carts are the same (set them both to 1 kg), what will the velocity of the second cart be compared to what the first cart had in an elastic collision? What is the velocity in an inelastic collision?

4. If the second cart has twice the mass of the first, what will the second cart’s velocity be compared to what the first cart started with in an inelastic collision?

Inelastic Collision Problems

For all these problems, the final mass is both masses added together (they stick together after the collision). This is called an inelastic collision. Elastic is when they bounce off each other (elastic ball).

1. A 150 kg lineman moving at 2 m/s hits a stationary quarterback whose mass is 50 kg. If the lineman holds on after the collision, how fast is the pair moving?
a) How much momentum is there before the collision?
b) how much momentum is there after the collision?
c) What is the speed of the two after the collision?

2. Lee has a mass of 46.5 kg and ice skates with a speed of 4.32 m/s. She collides into Mat (68.9 kg) who is standing still on the ice. They move off together holding on to each other. What is their final speed in m/s?

3. You shoot a 0.2 kg arrow at 50 m/s into a stationary wooden block that weighs 1 kg. If the arrow gets embedded into the wood, how fast will the block and arrow travel after the collision?

4. A girl, mass 70.0 kg, is running 3.0 m/s east when she jumps onto a stationary skateboard, mass 2.0 kg. What is the velocity of the girl and skateboard assuming they move off together?

Tricky Homework Questions:

1. The diagram above depicts a 2 kg mass colliding with and sticking to a second box. What is the mass of the second box?

2. A 0.2 kg apple has what momentum after it falls from a 15 m high tree?

3. A 1000 kg car accelerates from rest at 5m/s2 for 5 seconds. What is the car’s momentum after the acceleration?

Adding up the total momentum.
When things crash, momentum is conserved, meaning any momentum around before the collision is also present after the collision. It just gets transferred. So to solve a problem, you just add up all the momentum there is before a crash. That same amount of momentum must be present after the crash.

For each problem, draw a picture of what is happening, label the mass, velocity, and momentum in the picture, and do the calculations showing your work.

1a. If a 5 kg bowling ball is moving at +5 m/s toward a 1 kg bowling pin, how much momentum is present before the ball hits the pin?

1b. If the 5 kg ball comes to a stop after the crash, how much momentum must the bowling pin have after the collision?

1c. How fast is the bowling pin going after the impact?

2a. If a 1000 kg truck is moving at +5 m/s and a 500 kg car is traveling in the opposite direction at 10 m/s (-10m/s), how much momentum is present before the collision?

2b. If the car and the truck crash, how much momentum should be present after the collision?

2c. How fast is the 500 kg car moving after the crash?

3a. If two ice skaters stand on the ice holding hands, how much momentum is present?

3b. If skater 1 pushes the skater 2 away from him with a momentum of +65 kg-m/s. What should skater 1′s momentum be after the push?

3c. If skater 1′s mass is 65 kg, how fast is he moving after the push?

4a. If a 100 kg lineman is moving 3 m/s toward a 50 kg quarterback who is standing still, how much momentum is present before the collision?

4b. If the lineman hits the quarterback and holds on to him, how much momentum should be present?

4c. What should the velocity of the lineman and quarterback be after the collision (remember that the lineman is holding onto the quarterback so their masses should be added together)?

Momentum Carts Lab
Lab: Use the carts to do the following experiments. each experiment should include a drawing and an explanation of what happened.

1. Find the ends of the carts that has magnets that repel each other. With one cart stationary in the middle of the track, slowly push a cart into it. How fast does the second cart go compared to how fast you pushed it? Draw a picture of the collision and add velocity vectors to the drawing that represent the velocities (shorter vectors for slow and longer for fast).

2. Put a weight on the cart you roll into the other cart and try to give it the same velocity as in #1. How fast does the second cart go compared to how fast you pushed it? Draw a picture of the collision and add velocity vectors to the drawing that represent the velocities (shorter vectors for slow and longer for fast).

3. Take the weight of the first cart and put it on the cart being hit. How fast does the second cart go compared to how fast you pushed it? Draw a picture of the collision and add velocity vectors to the drawing that represent the velocities (shorter vectors for slow and longer for fast).

Momentum examples

Momentum Questions

1. A gun fires a bullet of mass 0.1 kg at 320m/s. What is the momentum of the bullet? What speed would a 5 kg bowling ball have to have to have the same momentum?

2. If an astronaut throws a 3.0 kg air tank with a velocity of 5.0 m/s, what is the momentum of the air tank? How fast would she have to throw a 1.5 kg hammer so it would have the same momentum?

3. A 2000 kg car going down the road at 20 m/s has what momentum? How fast would a 0.001 kg fly have to be traveling in order to have the same momentum? If the fly hit the car with this momentum in a head on collision, what would happen?

4. A 50 kg running back runs at 4 m/s toward the goal posts. What speed would a 100 kg lineman have to hit him in order to stop all his motion?

5. A 0.3 kg ball moving at 4 m/s has what momentum? If this ball runs into another ball with a mass of 0.6 kg, giving it all its momentum, what will the 0.6 kg ball’s speed be?

6. A diesel train locomotive weighs 500,000 kg. If it is traveling at 30 m/s, what is its momentum? How fast must you drive your 1000 kg car into it to stop the locomotive?

7. If all the people on the earth jumped off a 10 meter high building and hit the ground at the same time, how much velocity would be given to the earth when they hit? Do this as homework if you don’t complete it in class.