Work and Energy Study Guide

Previous scribe was abducted by aliens and hasn't scribed ever since, so I inherited his scribing powers under the "first come, first serve" rule.

The study guide is straightforward. Basic stuff. Grade 12 physics students can do this in their sleep.


10.1 WORK AND ENERGY STUDY GUIDE

Note: Capitalized words are the answers to fill-in-the-blanks.

Work
Work is the product of the FORCE exerted on an object and the DISTANCE the object moves in the DIRECTION of the force. The equation used to calculate work is W = Fd. In this equation, W stands for WORK, F stands for FORCE, and d stands for DISTANCE. Work has no direction, so it is a scalar quantity. The SI unit of work is the JOULE. When a force of one NEWTON moves an object a distance of one METRE, one JOULE of work is done. Work is done on an object only if the object MOVES. Work is done only if the FORCE and the DISTANCE are in the same direction.

Work and Direction of Force
If a force is exerted IN THE DIRECTION OF the motion, work is done. If a force is exerted PERPENDICULAR to the motion, no work is done. If a force is exerted at another angle to the motion, only the component of the force IN THE DIRECTION OF the motion does work. The magnitude of this component is found by multiplying the force applied by the COSINE of the angle between the force and the DIRECTION OF THE MOTION. When friction opposes motion, the work done by friction is NEGATIVE. When work is done on an object, ENERGY is transferred. Work is the transfer of energy as the result of MOTION. This transfer can be POSITIVE or NEGATIVE.

Power
Power is the RATE of doing work, or the RATE at which ENERGY is transferred. The equation used to calculate power is P = W/t. In this equation, P stands for POWER, W stands for WORK, and t stands for TIME. The unit of power is the WATT. One JOULE of energy transferred in one second equals one watt. This is a very small unit, so power is often measured in KILOWATTS.

1. Symbol for kinetic energy: K
2. Calculation of kinetic energy: mv^2/2
3. Symbol for work: W
4. Calculation of work: Fd
5. Statement that the work done on an object is equal to the object’s change in kinetic energy: Delta K = W
6. Equivalent to 1 kg*m^2/s^2: 1 J

7. Through the process of doing work, energy can move between the environment and the system as the result of FORCES.
8. If the environment does work on the system, the quantity of work is POSITIVE.
9. If the environment does work on the system, the energy of the system INCREASES.
10. If the system does work on the environment, the energy of the system DECREASES.
11. In the equation W = Fd, Fd holds only for CONSTANT forces exerted in the direction of displacement.
12. In the equation W = Fd cos theta, angle theta is the angle between F and the X-AXIS.


13. W > 0: B, E, F
14. W = 0: A, D
15. W < 0: C


16. What was the magnitude of the force acting on the crate? 30.0 N
17. How far did the crate move horizontally? 0.50 m
18. What does the area under the curve of this graph represent? work
19. How much work was done in moving the crate 0.1 m? 3.0 J

20. Rate of doing work: power
21. Unit of power: watt
22. Symbol for power: P
23. Calculation of power: W/t
24. 1000 watts: kW

Next scribe is KAMIL.

October 29, 2008: Work and Power

In today's class we finished the rest of the question in Concept-Development Practice Page 9.2.
The answer to them are:
4.
a) normal
b) normal

5.
a)Yes
b)Provides centripetal force for circular motion.

After that, Mrs. K handed back our lab and assignment (questions 4 and 5), with it she gave us a small booklet on our last unit in mechanics, Work and Energy, which contains a small introduction to Calculus. We only read the first 4 pages then right after we started a new lab relating to the equations mentioned in the booklet.

Page 1
Page 2
Page 3
Page 4

At the end of the class we were given a chapter 10 study guide.

Finally the next scribe is Vieteran!!

Centripetal Acceleration/Force Problems

Centripetalaccelerationworksheet

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Derivation of Centripetal acceleration

Derivecentripetalacc

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Tuesday, October 28th

Today in class we went over the Centripetal Acceleration assignment and the Centripetal Force assignment that was on the same sheet. Near the end of the class we also went over the Concept Development Practice Page (the one with the pictures).

Here are the answers for the Centripetal Force assignment:

1.A) 34.9 m/s
B) 24.4 m/s²

2. A) 18.85 m/s
B) 237 m/s²

3. 8 m/s²

4. 1.22 x 10^-5 m/s²

5. A) 0.52 m/s
B) 1.8 m/s2

Answers for the Centripetal Force questions on the back of the same sheet:

1. 27 N

2. A) 46.3 m/s²

B) 4.63 N

3. A) 157.9 m/s²
B) 78.95 N

Answers for the Concept-Developtment Practice Page (Acceleration and Circular Motion side):

1. A) Backward
B) Forward
C) Forward

2. A) Forward
B) Backward
C) Backward

3. A) Outward
B) Inward
C) Inward

4. Opposite

5. A) Faster
B) Increases

6. A) More
B) Increases

Answers for the Concept-Development Practice Page (Centripetal Force):

1. A) T
B) T

2. A) Inward
B) Yes
C) Yes
D) Yes

3. A) Fn pointing up, Ff pointing towards the left, Fg pointing downward
B) Ff
C) Ff
D) Ac is not zero

4. A) Ff
B) Ff

Aaand that’s about all we did for class today! Next scribe is…..Shelly

Derivation for Circular Motion Formulas

Deriving a formula for velocity, acceleration, and the centripetal force when in a circular motion...


LEGEND
v = velocity (or speed, if direction is not indicated)
d = displacement (or distance, if direction is not indicated)
t = time (interval)
R = radius
a = acceleration
a_c = centripetal acceleration
F = force
F_net = net force
F_c = centripetal force
m = mass


1.
The distance an object moves in a circular motion is the circumference of the circular motion, which is equal to 2*pi*R. Using the definition of circumference (c=π*2*r) and the definition of velocity (v=d/t), we can derive this formula: v=2*π*R/t.

2.
Draw the circular motion, two radii, and two velocity vectors. Add the two radii vectors to get the net radius. Add the two velocity vectors to get the net velocity.

3.
Since the change in radii over the radius equals the change in velocities over a velocity (ΔR/R = Δv/v), using the definition of velocity (v=ΔR/Δt) and acceleration (a=Δv/Δt), we can derive this formula: a=v^2/R.

4.

Using the acceleration formula that we recently derived (a=v^2/R), we can use substitute velocity with v=2*π*R/t to get a more fancy-looking formula for centripetal acceleration (a=4*π^2*R/T).

5.
Using Newton's Second Law of Motion (F_net=m*a), we can substitute acceleration with a=v^2/R to get the formula for centripetal force (F_c=m*v^2/R), which can be derived even further using v=2*π*R/t to get F_c=4*π^2*R/t^2.

• Centripetal Force lab is due and was handed in today.
• Centripetal Acceleration and Centripetal Force assignments is due tomorrow.
• Next scribe is ERIC.

Centripetal Force Lab

Today in physics class we did a lab on centripetal force.

In this lab the equipment that we needed was
glass tube 10 to 20 cm long, and about 1 cm outside diameter (tube should be fire-polished at both ends)
Nylon cord (about 1.5 m) size 4 stopper, 2hole 25 iron washers (about 0.06n each)
Stopwatch or watch with second hand
Alligator clip

The objective of the lab was
During this investigation you will study circular motion experimentally. Use the graphical analysis of circular motion to study the relationships between the centripetal force and the velocity of an object moving in a circular path and the radius of the path.

In the lab we had to connect a rubber stopper to one end of the string and on the other end we had to add a bent paper clip with washers connected to it you also need to put the alligator clips somewhere near the middle of the string.
We also had to time how many seconds it would take to get 30 revolutions for 5 washers, 10 washers, 15 washers, 20 washers and 25 washers.

Don't forget to do the calculations and the Interpretation on the sheet. Well that's all the next scribe will be ZEPH.

Free Body Diagrams-Circular Motion

Mole Day !

Hello physics lovers :)

Here's a summary of today's class!

First we corrected the Chapter 7 Study Guide (7.2 Periodic Motion Circular Motion) that was given the previous day. Here are the the answers:

If an object is moving with uniform circular motion, the speed is constant. Velocity is changing because the direction is changing. In uniform circular motion, the radius of the path is constant. The velocity is perpendicular to the radius and tangent to the circular path. Any vector that is tangent to the circle represents the instantaneous velocity at that point. All such vectors will have the same length, but different directions. The vector that represents acceleration is in the direction of the radius, pointing toward the center of the circle. Centripetal acceleration points toward the center of the circle. It is directly proportional to the square of the speed and inversely proportional to the radius of the circle. According to Newton's 2nd law, centripetal acceleration must be caused by a(n) force that acts toward the center of the circle. The force that causes centripetal acceleration is called centripetal force. If this force disappears, the object in uniform circular motion will travel on a path it is a(n) straight line tangent to the circle.

After that we corrected the Free-Body Exercise: Circular Motion,
here are the answers:




Then Ms. K handed out notes on Centripetal and Centrifugal Forces.

Centripetal force is the force that is necessary to keep an object moving in a curved path and that is directed inward toward the center of rotation. For example the car going around a curve there must be friction to provide the required centripetal force, if the force of friction is not great enough, skidding will occur.

Centrifugal force is the apparent force that is felt by an object moving in a curved path that acts outwardly away from the center of rotation like the the clothes being force against the wall of the washing machine.

We also got a hand out on Frames of Reference, that we read while Ms. K got the television for a video on Circular Motion.

Here are some videos I found on You Tube that I hope will help!

Look who I found, MR. SAME SAME !



It's Bill Nye the Science Guy!

PART ONE:


PART TWO:


PART THREE:



I hope this helped! Sorry for the late blog.
The next scribe for tomorrow is Richard,
you said to pick you.. you have all weekend :)

Goodnight Everyone!

October 22, 2008

For todays class, we started off by getting our tests back and going over them. And the answers were uploaded by Ms. K. After, we started a new unit called "CIrcular Motion". We were also given the Chapter 7 Study Guide Worksheet and the Free Body Diagram Worksheet and we were given the rest of the class to work on them.
And that is all for todays class.
Oh, and the next scribe is ROJUANE.

Momentum & Projectile Motion Test

Mom&Projtest

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Review Day

So today we went over that review sheet Ms.K gave.

Answers:
1)0.25m
2)7.83m/s
3)a)6.4s
b)203.65m
4)a)0.8s
b)0.82m
c)5.68m


Later in the class, she handed out a Transparency Worksheet.

THE TRAJECTORY OF A PROJECTILE
Answers:
1)Trajectory
2)Projectile
3)Vx = Horizontal Velocity; Vy = Vertical Velocity
4) Stays Constant
5)Increases due to gravity
6)None
7)Gravity is acting on the droplet. The droplet is acting on the earth, meaning the Earth is acting on the droplet.
8)None; Law 1 - An object in motion stays in motion
9)Gravity does not affect the horizontal velocity, and it affects only the vertical velocity.
10) Yes because mercury has a greater mass.

Our test is tomorrow, so good luck everyone and study hard!

Oh yeah, and before I forget, the next scribe will be Christine.

Friday, October 17, 2008

Today in class, we went over some answers in our chapter 7 study guide, on the section entitled "Objects Launched at an Angle" the answers are filled in the blanks in this order: positive, zero, negative, the same, reversed, horizontal, horizontal, vertical, equal, equal to.

We also went over the answers of the worksheet " Projectile Motion II" The answers are as follows:
Question one: 141.4 m
Question two: 10 m from flag
Question three:
a) 4.42 seconds
b) 55.25 m
Question four: 70 m/s
Question five:
a) 16.2 m/s
b) 11.5 m

We also got two worksheets to review for our test on Monday.
The next scribe will be Lawrence!

October 16, 2008

Today in class we were asked to finish all three of our labs ( coin lab, projectile motion lab, and our catapult lab) and also do a work sheet with questions relating to the catapult experiment, this is due tomorrow.

Francis will scribe next.

Wednesday, October 15, 08

On this day all we did in class was work on the catapult experiment which was due, and it took the whole class to get everything done. People who finished early worked on the projectile motion experiment and such.

Thats all


Kamil will be scribing next...

Catapult Pictures

physics

Good evening ladies and gentlemen...
Today's class was kind fun and mostly enjoyable by everyone.
It was a good thing that everybody was busy working on assignment.
First we corrected the projectile motion 1, then miss K. hand out analysis of the path of projectile lab which we all worked on the rest of the class.
Thanks every one and have good night.


Next to scribe is Mr. YONAS.

October 9, 2008

Today in class we corrected our fill in the blanks sheet, after we learned about Trajectories, we watched an example by Mrs. Kozoriz, then did our own lab, we have a lab sheet due on tuesday for that lab on Trajectories. Thats all for this thursday, enjoy your long weekend, and happy thanksgiving. and Jabahee will scribe for tuesday.

Wednesday, October 8, 06

Today we basically worked on conservation of momentum assignment that was due. Also we started a new unit which is, named projectile motion, and a study guide on chapter 7 was handed out as well.


For those who don't really get the idea of "Elastic And Inelastic Collisions" here is a great website that precisely demonstrates how they're played out.

Physics Oct. 6, 2008

Today we corrected chapter 9 study guide fill-in-the-blanks, chapter 9 reteachings, the study guide questions, and the chapter 9 review. We were also assigned a conservation of momentum worksheet and our project on projectile motion by constructing a catapult.

October 1, 2008 Blog.

Double Scribed : Say thanks. ;P

Today in class we were given time to finish the lab previously assigned on the 30th of September. The lab was supposed to be handed in by the end of class. (By the way, the last question on the lab is confusing but if you think about the recoil it'll be alot easier).

We also corrected the questions in the "Duck Book".

50.
Jf = J1 + J2.
= (1/2 ( 100 N [G])) + [100N [E] (15s)]
= 250N + 1500 N
= 1750 N. [E]

b)
A= 1/2bh
= 1/2 (4.0x10^-2 s ) ( 15 N )
= 0.3 Ns.

c)
A=1/2bh
= 1/2(5)(-10)
= -25 Ns.

A2 = bh
= 12.5(-10)
= -125 Ns.

A3 = 1/2bh
= 1/2 (10)(-10)
= 1/2 (-100)
= - 50 Ns.

At = A1+A2+A3
= -200 Ns.

51.

(1/2 x - 90 x .03) + (120 x 0.2 ) + (1/2 x 75 x 0.4)
= 25.5 N.

Other than that? We were given extra assignments to help us get practice on the topic impulse and momentum.

Assignments / Homework :

1. IMPULSE AND MOMENTUM hand-out.
2. Complete "9 Study Guide."

That's pretty much it for the class besides me, Benchman and Lawrence having an arguement/discussion about the lab.

The next blogger like I said in the previous post I made will be chosen tomorrow.

September 30, 2008 Blog.

September 30 :

1. Corrected the first page of the "9 Study Guide".

Here are is the first page's answers :

1. B.
2. B.
3. B.
4. A.
5. D.
6. B.
7. D.
8. B.

Page 2 Answers (The back of the first page) :

9.
30 km/h right.
V = 0 m/s.
Impulse to the left.

10. V = 0 m/s.
V = 30 km/h.
Impulse to the right.

11. V = 0 m/s. (Backing up)
V2 = 5 m/s left.
Impulse to the left.

12. V = 5 km/h to the left.
V2 = 0 m/s.
Impulse to the right.

2. Completed a lab involving box carts and was due today.

The next blogger is : Anyone who wants to blog because I don't know who did or didn't.