Talking Work-Energy Assignment

Come up with a scenario of your own based on the examples we have been looking at in class while looking at work and energy. You should think of something that you UNDERSTAND, but that is CHALLENGING to you. You will be presenting your scenario to the class and will be assessed on your ability to explain it clearly, correctly and in an interesting fashion. Feel free to use diagrams and equations in your explanation. You will also be assessed on how challenging your example is and how well you display understanding of work, energy transfer and the different kinds of energy.

Rubric

	4	3	2	1
How challenging is my example?	My example contained at least one example of work and more than four kinds of energy (including at least one kinetic and one potential). I calculated the work and energies where ever possible and showed an understanding of each case of energy transfer and conservation.	My example contained at least one example of work and three or four kinds of energy (including at least one kinetic and one potential). I calculated the work and energies in a couple of cases and showed understanding of more than one case of energy transfer and conservation.	My example contained one example of work, kinetic energy and potential energy. I calculated the work or one of the energies and showed understanding of one case of energy transfer and conservation.	My example lacked calculations or missed work or kinetic or potential energy.
How much have I displayed my understanding?	I understood all or almost all, of my example and could answer all, or almost all, of the questions asked about it correctly.	I mostly understood my example and could answer most of the questions asked about it correctly.	I understood my example ok and could answer some of the questions asked about it correctly, but made some major mistakes.	I did not understand my example.
How well did I present my example?	I was clear, complete and interesting.	I was clear and complete.	I was usually clear and mostly complete.	I was hard to understand and missed a lot of stuff.

A 12/12 example

Scenario: I carry a 500 g ball (initially at rest) up a hill (where it is again at rest) and then roll it down to the bottom. In climbing the hill my altitude changes by 100m. I will ignore friction as the ball rolls down the hill. When it reaches the bottom of the hill the ball will collide with a tree and come to rest.

Explanation:

(The comments in brackets would not be required in the explanation to the class unless you were asked to explain.)

The ball starts at rest at the bottom of the hill, so it has zero kinetic and zero gravitational potential energy.
In carrying the ball up the hill I increase its potential energy due to gravity by an amount 490J (Calculated using GPE=mgh. Here, m=500g=0.500kg and h=100m, so GPE=0.500kg*9.8m/s²*100m=490J. ΔGPE=+490J.)

3. Since it starts and ends at rest the change in kinetic energy for the ball is 0J. (The ball begins and ends its trip up the hill at rest so the KE=0 at the beginning and the end. ΔKE=KE_f – KE_i = 0J - 0J = 0J.)

I do 490J of work in carrying the ball up the hill. (The work I do in carrying the ball is given by W_{Net from non basic forces}= ΔKE + ΔGPE = 0J + 490J = 490J.)
When I release the ball at the top of the hill it will begin rolling down, which will mean that the GPE of 490J is being transferred into linear KE and rotational KE of the ball.
At the bottom of the hill the total KE (linear plus rotational) of the ball will be 490J. (No other force acts except the normal force as the ball is rolling. The normal force is perpendicular to the motion, so it does no work on the ball. Since, W_{Net from non basic forces}= ΔKE + ΔGPE, and the net work is zero here, ΔKE + ΔGPE = 0. The ΔGPE=-490J in rolling down the hill, so the ΔKE=+490J.)
In striking the tree the KE becomes vibrational energy (sound and heat).