Friday, September 17th 2010

Grade 12 Mechanics Unit: Acceleration Test (Answers):

1) Step 1: Square both sides of the equation
V2² = V1² + 2V1at + a²t²
Step 2: Factor out 2a from the last two terms
V2² = V1² + 2a(V1t + ½at²)
Step 3: Substitute a term in the equation given in step 2
V2² = V1² + 2ad
Step 4: The equation is _____
V2² = V1² + 2ad

2) V1 = 40.0km/h ÷ 3.6 = 11.11m/s
a = -2.3m/s²
t = 2.7s
d = ?
V2 = ?

2a) d = V1t + ½at²
d = (11.11)(2.7) + ½(-2.3)(2.7)²
d = 21.6m

2b) V2 = V1 + at
V2 = 11.11 + (-2.3)(2.7)
V2 = 4.89m/s

3) V1 = 0m/s
a = 0.300m/s²
d = 25.0m
V2 = ?

V2² = V1² + 2ad
V2² = 0² + 2(0.300)(25.0)
V2² = 15
V2 = 3.87m/s

4) motorist = 80.0km/h(W)
police car = 95.0 km/h(W)

4a) motorist - police car
80.0 - 95.0 = 15km/h(E)

4b) police car - motorist
95.0 - 80.0 = 15km/h(W)

5) airplane's airspeed = 2.0 x 10²km/h(E)
approching destination = 15°(N of E)

5a) tan15° = 200 ÷ wind speed
wind speed = 200 ÷ tan15°
wind speed = 53.6km/h

5b) c² = a² + b²
speed approaching destination = (2.0 x 10²)² + (53.6)²
speed approaching destination = 207km/h

6) V1 = 25m/s
t = 1.45s
a = -8.5m/s²
V2 = 0m/s
d = ?

reacting to child and applying the brakes:
d = Vt
d = (25)(0.45)
d = 11.25m
after applying the brakes:
V2² = V1² + 2ad
d = V2² - V1² ÷ 2a
d = (0)² - (25)² ÷ 2(-8.5)
d = 36.76m
total distance = 11.25m + 36.76m = 48.0m

_____________________________________________________

Equilibrium: When an object has zero acceleration, meaning that the object is at rest or moving at constant velocity
Free Body Diagram: A drawing that represents the object and the forces acting on it

Steps to Drawing a Free Body Diagram:

1) Focus on the object you will be studying. If there is more than one object in the drawing, do each seperately.
2) Begin drawing the free body diagram by looking at only the desired object. The drawing will show where forces are applied to the object, so draw those forces on your free body diagram in exactly the same direction thats shown on the drawing.
3) Draw x and y axes on your free body diagram so you will be able to analyse the diagram. Try to draw your axes so that as many forces as possible are close or directly on the axes. It will help when calculating.
4)When the situation is equilibrium, make sure that the x and y components of the forces will be equal to zero when added.
5) Finally, solve for the unknown quantities.

_____________________________________________________

In class we received the 'Grade 12 Physics: Dynamics Unit' booklet, some of us recieved this booklet after finishing the Acceleration Test on Thursday. We read pg.1, completed pg.14, and completed #1 on pg.16. For homework we were assigned pg.12 & 13 (Free Body Diagrams) and #2-5 on pg.16 & 17 (Static Equilibrium Problems).

Test Day

Test on Acceleration. How did you do?

Cosine Law

Cosine law example

View more documents from ekozoriz.

Monday, September 13, 2010

First we began our class with handing in the assignment from Friday, titled "Grade 12 Physics: Acceleration Assignment" (which if you haven't, reminder that you should!) and copied and checked answers 8 - 11 on the practice worksheet titled "Grade 12 Physics: Acceleration II."

The answers are as followed :
(Note: Thanks Amy, and I hope you like the colours added.)

8b. = 121m
8c. = 391m
8d. = 946m
9. = 15m
10. = 1350m
11a. = 15.4s
11b. = 427m
11c. = 200km/h

For full, see a friend or Ms.K.

Once finished, we went back to the first booklet we received titled, "Grade 12 Physics Acceleration & Relative Velocity" and went over page 6 - 9, doing the questions along the way. Don't worry if you weren't there, all the answers are stapled along with the booklet on page 11.

Page 6 extending to 7 is the lesson about relative velocity.

The concept of relative velocity can be a bit confusing, but with a little more understanding it can be easy.

It's the relationship between 3 different velocities, that can be different depending on the question. In the example included in the booklet, there are the velocities of a passenger on a train, the train itself, and someone standing on the ground watching the train.

To the passenger, who is walking to the front of the train, their velocity is +2.0 m/s.
Note: The + sign indicates direction, so if the passenger was walking towards the rear, the velocity would be -2.0 m/s.

The train's velocity, to the person on the ground, is +9.0 m/s.

We can calculate the velocity that the person the ground can see, or any of the three as long as we have any 2 velocities.

The formula that can be used is:

Vpg = Vpt + Vtg

Vpg = (2.0 m/s) + (9.0 m/s) = 11 m/s

p = passenger, t = train, g = ground.

Each velocity has letters in the subscript that are in relation to the objects in the question. Look at the bottom of page 6 for more details.

At the end of page 7 there is a small chart which can be filled out to find the answer.

So on the next page, 8 , there are two diagrams with a matching sheet of questions. The questions are pretty straight forward, but it's never bad to take a second check on the answer key.

For homework, we were assigned two things:

1) Page 10 of the booklet, for practice. (Answers included in the key)

2) A relative velocity sheet with 7 questions which you can get from Ms.K, if you don't already have it, which we will correct in class.

Well that concludes our day, and I will come back to fill in those answers, sorry everyone! Reminder, TEST ON THURSDAY! So study, study!

-Sakhone P

FRIDAY, SEPTEMBER 10, 2010

For the start of the class, we went over one of the worksheets that was given out the yesterday that didn't have the answers.

[Please see Amy's post for the original sheet].

We worked it out and put all the answers on the white boards.

I've recorded down the answer for those who missed the class or missed an answer and would like to check it over:

We then received another worksheet, but this time instead of working it at home, we worked it together as a class with Mrs. Kozoriz on the SmartBoard.

The sheet that was given out:

Answers to the following worksheet:

Here, we use one of the formulas of finding velocity.

D.B. stands for Donovan Bailey and M.J. stands for Michael Johnson.

Mrs. Kozoriz also asked us how come Michael Johnson ran the 200-m faster than the 400-m. Well, because he had to do both runs! Total of 600-m and of course he would be tired and slow down !

Here, we used the same formula as we used for question one, but we rearranged it so that we could find the distance instead of the velocity.

To change the units of km/h to m/s, we have to divide the number in units of km/h with 3.6 .

** We have to make sure to change the units or else our answer will be wrong ! **

Here we also have to find the distance, but this time we use a different formula to find the distance. This formula uses both the velocity instead of one to find the distance.

Here, we now have acceleration given to us to help us find the final velocity.

Here, we use another formula to find the length of time.

It's also the same formula that we used to find the answer to the previous question, but again, we rearranged it to help find the time instead of the velocity.

What's different here, is that we have a negative acceleration.

Although it's negative, we don't do anything different, so don't let the negative sign throw you off!

For this question, it consists of 2 steps.

First we find the distance using a different formula.

Make sure you use a formula that doesn't use the final velocity to find the distance because we have to find that also.

Here, we assume that the final velocity equals to zero because it slows down to a stop.

Since the time was not given to us in the question, we have to use this formula to help us find the distance instead.

Although question 8 has four parts, we only went over how to do the first one, because once you know how to do the first one, the rest are worked out the same and should be easy to solve.

The worksheet [Gr.12 Physics Acceleration Assignment] that was given out on Wednesday, September 8th had answers given except for question 5. a) & b).

Amy had posted the worksheet and the answers but she didn't have the answers for number 5 because it was given in today's class.

So I'm just reposting the worksheet with the answers for those who might not have seen on Amy's previous post followed by the answers for question 5:

HOMEWORK :

Since we stopped after question 8) a. in class with Mrs. Kozoriz, we're left of to finishing the rest of question 8 to question 11.

She also gave us another handout to work on which is due on Monday, September 20! :

That's all that we did today !

Hope you enjoyed this post. Good luck and see you on Monday ! (:

- Kim

Amy's Scribe Post (Thursday, September 9, 2010)

Hello, my fellow students. I am gladly to present you our class' very first scribe post on the blog today. To start things off, the first thing we did in class was have Ms. Kozoriz review some simple formulas that we learned from grade 11 physics.

These equations can be found from finding the slope from a distance-time graph (for velocity) or a velocity-time graph (for acceleration).

The second thing that Ms. Kozoriz explained in class was how to derive equations from our handout given to us yesterday. These equations can be found on the formula sheet given as the first four under the section "Mechanics."

These equations can be rearranged to find the thing we need by simply rearranging the constants (using either multiplication/division) to find what we want.

Ms. Kozoriz also pointed out that velocity 1 equals to zero.

The next thing we learned was the Derivation of Acceleration Formulae. This can be explained through the diagram below:

As you can see, we can obtain the displacement from the graph by simply using the formula we learned in grade 11 physics when d=vt.

Ms. Kozoriz had then given another diagram to use as an example showing the same idea explaining that when finding two different displacements and combining them together, it gives us one of our derived equations where each half represents the shape of the diagram.

An overview of the diagram above:

Finally, Ms. Kozoriz taught us how to derive one of the last equations.

That concludes the lesson of Thursday, September 9, 2010.

HOMEWORK

Ah, the most important part of the day. Today Ms. Kozoriz had handed out 2 sheets of questions with a total of 20 (10 on each sheet). In case you did not get one (for some reason..) here are the the links for the 2 homework sheets.

Homework sheet 1 & Homework sheet 2 (with answers)

In that case, this is an end of my scribe post. Thank you to those who've taken the time to read what I have to share. Please leave some comments :)!!!