Reading Quiz

Question 1:

Answer:

1. There is gravitational and kinetic energy. Assuming no friction, when the pendulum is at its highest point, it is at rest and has only gravitational energy. When it falls, it loses gravitational energy and turns it into kinetic energy, which allows the pendulum to swing back up 20 cm on the other side.
2. When you lift the pendulum, it now has gravitational potential energy (1960J). When you release the pendulum and it swings toward its initial position of hanging straight down potential energy is transfered into kinetic energy. At the lowest point in its swing, the gravitational potential energy is zero, and all its energy has been transferred to kinetic. As it swings past the lowest point, the pendulum transfers energy from kinetic back into gravitational potential energy. At the maximum height on the other side (20cm without air resistance), all its kinetic energy has been transferred back into gravitational potential energy. This pattern continues infinitely according to Newton's Frist Law of Motion, however in reality the pendulum will eventually stop swinging as a result of the outside force of air resistance on it.
3. You exerted an upward force (using kinetic energy) to pull the mass on the pendulum 20 cm up. Then you released the pendulum bob and gravitational energy pulled the bob down. Then the pendulum swung downward and the kinetic energy increased as it picked up speed while gravitational energy decreased to 0 as it reached the lowest point in its swing. The kinetic energy then equals the gravitational energy at the top and the pendulum swings up to the other side. The energy transfers from kinetic energy to gravitational energy, slowing down until it stops at a height of 20 cm with the original gravitational energy and the pattern repeats.
4. At the top of the arc, the mass has the greatest gravitational energy and no kenetic engergy. As it moves down, ketetic energy increases and gravitational energey decreases. At the bottom of the arc, ketetic energy is at its greatest and so the ball is moving the fastest. The gravitational energy is at its least.
5. The pendulum has zero speed and zero kinetic energy at the top of its swing and at the bottom. Its gravitational energy is largest at the top of its swing and smallest at the bottom. Its maximum speed is reached at the bottom of its swing.
6. The pendulum continues to swing back and forth. IF there was no friction and no outside disturbance, it would keep swinging forever. Because the height of the bob chsnges, its gravitational energy changes as well leading to energy of motion, or kinetic energy.
7. When you lift up the pendulum the 20cm, you do work on the pendulum and give it gravitational energy. When you release the pendulum, the gravitational energy is slowly transformed into kinetic energy. When the bob is at the bottom of the arc, its energy is entirely kinetic instead of entirely gravitational. In between the tops and bottom of the arc, the energy is a combination of both types of energy.
8. At the top of the pendulum's swing, at its maximum height, it has its largest gravitational energy but zero speed and zero kinetic energy (energy of motion). At the bottom of the pendulum's swing, it has its smallest gravitational energy but maximum speed and maximum kinetic energy. There is no net change in total energy.
9. When hanging straight down, it has zero kinetic energy. While it is held at 20 cm, it has the greatest gravitational potential energy, and as it is released and eventually reaches the bottom of the swing it has growing kinetic energy. As it swings upward from the bottom, it gains gravitational potential energy and loses kinetic energy.
10. First you are exerting a force which counters gravity on the pendulum to raise it 20cm up which makes the pendulum accelerate up until it is at rest at 20cm. Once it is released it its gravitational energy accelerates it constantly downward at a rate of 9.8m/s^2 until it reaches the bottom and begins to decelerate until its speed again reaches 0.
11. At rest and at the top of its swing, the mass has the greatest gravitational energy. As it is released its velocity increases as well as its acceleration and the gravitational energy is then transferred into kinetic energy. As it reaches the top of its swing on the other side, the energy changes into gravitational energy again and the process repeats forever. The pendulum would actually keep swinging forever if there were no other outside forces acting on it.
12. At the bottom of its arc, the pendulum would have a velocity of 9.90 m/s^2. Since total energy at the top of its swing [gravitional energy (19.6 J) + kinetic energy (0 J)] must be equal to total energy at the bottom, kinetic energy must be equal to 19.6 J. Since kinetic energy = 1/2 mv^2, 19.6 J = 1/2 (10 kg) v^2, and v = 9.90 m/s.
13. At the pendulums top most point, 20cm up, it has a Gravitational energy potential of 10kg x 10m/s2 x .20m = 20N/m. This energy is transformed into kinetic energy as soon as the mass starts to fall, reaches its pinical of kinetic energy at the bottom of its swing, and then fully returns to gravitational potential energy at the height of its swing agian.
14. Since the pendulum starts from rest, it starts with zero kinetic energy, and a large gravitational energy. At the bottom of the swing, its gravitational energy is smallest, and its kinetic energy is greatest. The total energy will be conserved if the gain of kinetic energy exactly equals the loss of gravitational energy.
15. V = [2 x 10m/s x .2m]^1/2 = 2 m/s
16. At the top of the swing, the speed of the mass is zero, and thus the gravatational energy is at its largest and the kinetic energy is zero, since it is not moving. At the bottom of its swing, the kinetic energy is at its greatest, and the gravitational energy is at its smallest. There is no net change in energy.
17. When the ball is lifted the original 20 cm, energy is being transferred to the ball from the person lifting it. The amount of the energy transfer would be equal to the gravitational potential energy that the ball now has. Once the ball is dropped, gravity acts on the ball and its gravitational potential energy decreases as it approaches the bottom of its arc. At the same time, kinetic energy is increasing as the ball picks up speed, and at the bottom, it has no potential energy and all kinetic energy. Then, as the ball rises toward the other end of its arc, it picks up gravitational potential energy and loses kinetic energy until it stops and falls again. Assuming no air resistance or other outside forces, this motion would continue, with the ball rising to 20 cm high at each end before descending again.
18. Since the initial gravitational energy plus inital kinetic energy is equal to the final gravitational and final kinetic energy, if kinetic energy increases then gravitational energy must decrease and vice versa. So when the pendulum is going up, kinetic energy is decreasing but gravitational energy is decreasing. The opposite is true when the ball is on its way down.
19. When lifting the pendulum to the top of its path it has gravitational energy pulling it downward. When the pendulum is dropped its gravitational energy is transferred into kinetic energy as it gains speed. Then as it loses speed at the top of its path on the other side it comes to a momentary rest where it was no kinetic energy and all gravitational energy again. The process then repeats.
20. When the pendulum makes its swinging motion, there are two energies: kinetic (the enery of motion) and gravitational. When the pendulum is at the top of its swing, it stops moving (has no speed) and therefore it has no kinetic energy. At the top of its swing, it has its maximum gravitational energy. As the pendulum swings down, it transfers to kinetic energy and the gravitational energy decreases. At the bottom of its swing, it has the maximum kinetic energy, and its least amount of gravitational energy.
21. As you lift the pendulum it gains gravitational energy. As you release it from 20cm from rest there is no kinetic energy but 2000J of Gravitational energy. As it is released it gains speed and kinetic energy but loses gravitational energy. When it is at the bottom of its arc there is no gravitational energy but 2000J of kinetic energy. As it starts to rise it loses kinetic energy and gains gravitational energy...this cycle repeats.
22. the gravity energy is largest at the top of the ball's motion when the speed energy is zero, meaning the kinetic energy is zero. At the bottom of the its motion, the speed is highest so there is kinetic energy but gravity's energy is the least. These energy transformations continue as long as the ball moves in this fashion.
23. Since the object changes height during its swing, its gravitational energy changes. At the top of its swing the speed is 0 and therefore there is 0 kinetic energy and its gravitational energy is at its heighest. At the bottom of the swing the object is moving at its fastest speed and thus the gravitational energy is at its smallest.

Question 2:

Answer:

1. 19.8 m/s
2. Since the gravitational potential energy at the beginning of its swing is equal to 1960J, and it is at rest and therefore has not kinetic energy, all that potential energy is transferred to kinetic energy at the bottom point in its arc. This means that the kinetic energy of the pendulum at its lowest point would be equal to 1960J. Plugging this as well as the mass of 10 kg into the equation for kinetic energy, you get that the bedulum would have a velocity of 19.8 m/s at the bottom of its arc.
3. v = (2g(H-h))^(1/2) v = (2*9.8*.2)^(1/2) v = 1.9 m/s
4. 1.98 m/s
5. .63 m/s
6. about 6.9 feet per second
7. We can use U=mgh to find the total energy in the system. 10kg times 9.8 N times .2m is 19.6 joules. We can use this amount of energy in the kinetic energy formula to determine the velocity. We know that U=1/2mv^2, so if we rearrange the equation for velocity, we know that the velocity is the square root of 19.6 divided by 1/2 times 10kg. So, v^2 is 3.92, and the velocity is 1.98 meters per second. Therefore, the speed that the bob would be moving at the bottom of its arc is 1.98 meters/second.
8. I'm confused about how to use the equation.. I think the right equation for this type of problem is on pp. 30-31.. I know that for this problem the maximum height H is 20. What is h, 0? I don't know exactly which values correspond with which variables.
9. 1.98 m/s so approximately 2 m/s.
10. using the formula v=[2g(H-h)]^1/2 [2x9.8m/s^2(20-0)]^1/2= the pendulum would be traveling at a rate of 19.8m/s at the bottom of its arc.
11. It would be going about 1.98 m/s.
12. In solving the previous problem, if we use a height of 20 cm or .2 m for the top of the swing, the height at the bottom would be 0 m. This means that the gravitational energy would theoretically be zero, but is this really possible or just a theoretical assumption to solve the problem?
13. mg(hi) + .5m(v^2i) = mg(hf) + .5m(v^2f) 10kg(10m/s^2)(.2m) + .5(10kg)(0m/s) = 10kg(10m/s^2)(0) + .5(10kg)(v^2f) 20N/m = 5kg V^2f = 4m/s^2 Vf = 2m/s
14. I wasnt really sure how to do this problem, and what equation to use.
15. I would like to go over the pendulum/kinetic energy equations.
16. 35.8 cm/second
17. It would be going 1.9799 m/s.
18. [2(10 m/s^2)(20 m)]^.5 or 20 m/s
19. 1.98 m/s
20. I'm a little confused by this point as to what i'm doing, honestly. I think I would have to use the equation H= h+ (V^2/2g). So, when i calculate that, where H=20cm, h=0, g=32, and V is the unknown velocity(speed). In order to have V on one side of the equation, we have to move things around to make V=[2g(H-h)]^1/2. When I solve for v here, I get 8m/s^2.
21. there would be 2000J of kinetic energy so it would be going 20 cm/s
22. 0=20 + 0(t) + .5(9.8)(t^2) so, -20= (4.9)(t^2) so, -20/4.9 = t^2 so then, t=square root(20/4.9)= 2.02s. So now that we have the time, we can find the velocity: Final velocity = 0 + 9.8(2.02s) so then, final v = 19.796 cm/s.
23. Potential Energy + Kinetic Energy at the top = Potential Energy + Kinectic Energy at the bottom. So the velocity at the bottom of the arc = 5.6 m/s.

Question 3:

Answer:

1. I found the part with the pendulums a little confusing. I had a hard time understanding the equations. The concepts were not too bad, but the equations were hard to figure out.
2. I understood the concepts and equations from the reading.
3. I understand these concepts well. I would like to do a hands on demonstration of these principles.
4. I think the formulas are a little confusing.
5. None
6. I was a bit confused on the pundulum example and how they reached some of the calculations.
7. none
8. See above.
9. I didn't understand in the first few paragraphs when they said speed could be negative. Speed is a scalar quantity, and therefore has no direction. I guess they meant to say velocity is negative in this case, but I was not sure.
10. I felt most of this reading was fairly straight-foward.
11. I think I understood pretty much everything from the reading...although at times the wording in the reading became a little confusing as to how the equations came about.
12. I think I am fairly clear with the previous material.
13. The section at the end about radioactivity and nuclear energy was somwhat confusing, but I understand the idea that even when scientists thought the conservation of energy law was not holding up in this situation, it eventually did. And so these laws of conservation always hold up.
14. i was confused about a lot the equations they mentioned in the packet, especially since they showed how they got the final equation. I was also unsure of what to use each equation for and what values to plug in where.
15. I am still struggling with how to draw the graphs of vel vs. time and accel vs. time. Also, I am having difficulty with the free body diagrams.
16. I am confused with the notation of the third equation on page 32.
17. --
18. I think everything was pretty clear from the reading, however I'd like to spend some quality time on pendulums and how energy is tranferred.
19. I would like to go over the second question on the online quiz i'm not sure if I did it correctly.
20. I really am having a hard time with this, since I'm not sure if I did question 2, and the second half of the reading was very hard to understand. There were some points where it assumed we didn't know basic math (pg.27) where it showed us that g(tf-ti) is the same as g X(tf-ti)to moving really fast through the explanation of the equation and how to use it.
21. some of the equations explaining how to get to the conservation equation were confusing.
22. none.
23. explain the KE and PE formals.

Question 4:

Answer:

1. not much Have a nice weekend
2. I feel like I am still okay with course content so far.
3. calculating work for pushing objects up ramps
4. Nothing
5. None
6. nothing at this time.
7. none
8. The concept of splitting up horizontal and vertical velocity as necessary in an equation(s).
9. Force diagrams of a person in an elevator
10. I may be a little confused on the force/mass/ramps activities still.
11. I understood everything in class.
12. I dont think i'm having difficulty with anything in particualr from any previous classes.
13. During the previous class we worked on group exercise problems, i think i understood the answer once we discussed it as a group or once you gave us hints, but i would have trouble finding the correct answers myself. Ill practice them a bit more and ask you about the ones i need further explaination on.
14. previous questions have been answered... thanks.
15. --
16. I think everything is pretty clear.
17. Nothing.
18. I think i'm doing alright with things. I think it would be helpful if we wrote down all the equations on the board that we will be answering questions on so far. Also, i'm not quite sure about the problem on page 15 (the lifting an elephant with a baby).
19. i think im pretty caught up
20. well, i think that there is an easier way to do question 2 than the way i did it. so maybe i'm having difficulty finding the easier way.
21. ramps