Monthly Schedule

(AP Calculus AB, Period D)

T 3/1/05

HW due: Read to end of §7.3 (omitting Exploration 2), and solve the following problems:

1. Compute the volume of the loaf of bread displayed in class (trapezoidal base bounded by (0, 0), (5, 0), (5, 2), and (0, 3) in the xy-plane, with equilateral triangles for cross sections). Linear dimensions are in inches.

2. Compute the volume of a bagel having inner diameter of 1.5" and outer diameter of 4.25". As demonstrated in class, the cross sections are either cylinders with cores removed (if you perform plane slicing from top to bottom), or ordinary cylinders (if you perform radial slicing). The second approach is easier, but you will have to invent a technique that is not in the textbook. If you listened carefully during class, you know how to set up the radial slicing method as a d
q integral and a variable-factor product involving circular cross sections. (If you can swing it, the radial slicing method is definitely easier. Although plane slicing also works, plane slicing involves consideration of the inner and outer radii that can get a bit confusing.)

 

W 3/2/05

No additional HW due.

 

Th 3/3/05

HW due:

1. Prove that for any parabolic arch of base b units and height h units, the area equals ⅔bh. If you cannot do this, then do the following simpler problem instead: Use FTC1 to prove that the area bounded by the parabola y = 9 – x2 and the x-axis equals 36 square units.

2. Compute the volume of the paraboloid created by revolving the parabola y = 25 – x2, y
³ 0, about the y-axis. Use the following two methods (the first is easy, the second is harder):

(a) Use the method of plane slicing, using planes perpendicular to the y-axis.
(b) Use the method of cylindrical shells, using shells whose axis is the y-axis.

3. Recall Mr. Hansen’s loaf of bread, which used a trapezoidal base bounded by (0, 0), (5, 0), (5, 2), and (0, 3) in the xy-plane. This time, assume that the cross sections along slices perpendicular to the x-axis are not equilateral triangles, but instead parabolas each of whose height equals its base. Compute the volume. (Linear dimensions are in inches.)

4. Recall Mr. Hansen’s angel food cake, which is a solid of rotation generated by revolving an isosceles trapezoid about the y-axis. The isosceles trapezoid is bounded by the points (1.5, 0), (4.5, 0), (4, 4), and (2, 4). Compute the volume two ways (the first is hard, the second is easy):

(a) Use the method of plane slicing, using washers perpendicular to the y-axis.
(b) Use the method of cylindrical shells.

 

F 3/4/05

HW due: Finish up all previously assigned problems, and add the following easy one:

4.(c) Repeat the angel food cake problem, this time using radial slicing.

 

M 3/7/05

HW due: Work the following review problems.

 

1.         Write a paragraph in which you describe how to perform plane slicing to calculate volume. Try to write this without referring to your notes or to the textbook.

2.         Let R be the circular region bounded by x2 + y2 = 16 in the xy-plane. R is the base of a solid such that each cross section (when the solid is intersected by planes perpendicular to the x-axis) is an isosceles right triangle. Each such isosceles right triangle has as one of its legs the segment between the points (x, –(16 – x2)½) and (x, (16 – x2)½). Show that the volume of the solid created in this fashion is 170⅔ cubic units.

3.         Explain the formula V = ò 2pr h(r) dr, which is a formula that is sometimes useful for calculating volumes. In other words, explain what 2pr represents, what h(r) represents, what dr represents, and what Riemann sum is being invoked.

4.         What method is represented by the formula V = ò 2pr h(r) dr? Is this formula required for the AP exam?

5.         For a regular square pyramid, let s = side length of square base, and let h = height, i.e., the perpendicular distance from the apex to the plane of the base. Several years ago, in geometry class, you learned that V = ⅓s2h for this pyramid. Use plane slicing to prove the formula. If you can’t do this (because of algebra errors, or whatever), then use plane slicing to prove that the volume of a regular square pyramid having a 5-by-5 base and height 12 units equals 100 cubic units. Do not use the formula from geometry; use plane slicing. (It does not matter whether you use slices to create cross sections that are squares, triangles, or trapezoids. However, squares are the easiest.)

6.         The right triangular region bounded by the origin, the point (3, –2), and the point (7, 4) is revolved about the y-axis in order to create a solid of revolution. A cross section through this solid, in the xy-plane, would look like a bow tie.

 

a.          Solids of revolution are important to study, in part, because they are commonly used in the engineering of real-world objects. Why? Try to think of at least two reasons.

b.         Compute the volume by radial slicing. (This is probably the easiest way. However, for obscure reasons that are beyond the scope of our course, you must use as your radius the value r = 10/3 since the centroid of the triangle is located at (10/3, 2/3). If you have forgotten what a centroid is, you could briefly review geometry. However, if you prefer, you may simply use my value for the radius, compute the volume, and move on. The answer is approximately 272.271 cubic units. If it takes you more than a minute or two to compute that value with your calculator, I expect to receive an e-mail message from you ASAP.)

c.          Compute the volume by plane slicing, using planes perpendicular to the y-axis. (This is probably how the AP would suggest that you perform the task.)

d.         Compute the volume by cylindrical shells. (This is slightly easier than (c) but harder than (b).)

 

After you have worked these problems, I strongly recommend that you work some additional problems to build your proficiency and speed. There are many in the textbook, or you can try an actual AP problem. Read problem #1 from the 2002 exam as an example of what you are supposed to be able to do in 15 minutes. (Note: Acrobat Reader is required in order for you to view that link.)

 

That’s certainly enough problems to keep you busy, but here is another optional one that is fairly interesting. Use the definition of average value of a function to prove that if a regular square pyramid (see #5 above) is sliced with planar cross sections parallel to the base, the average cross sectional area is ⅓ the area of the base.

 

In class: Review.

 

T 3/8/05

Test on §7.3 and Average Value of a Function. Note that §7.2 will in effect be tested again, since many the volumes you compute involve calculating areas of cross sectional surfaces, and frequently those cross sectional areas are complicated enough to require the techniques of §7.2. (That is why §7.2 appears before §7.3.)

Here are the setups from the two problems we did not get to at the end of class Monday:







 

W 3/9/05

No additional HW due today.

 

Th 3/10/05

HW due (as announced in class): Read §7.4. Since this announcement was not posted in writing until 8:45 p.m. Wednesday, I guess that technically you are exempt from the reading assignment. However, don’t you have enough days off already this week and next? It would make me happy if everyone had at least read the section before class today.

Please inform me of any grade-related issues for the third quarter by no later than noon today.

 

F 3/11/05

Day of rest (also last day of third quarter).

 

M 3/14/05

Career Day (no class).

The BIG TRIG CHALLENGE in Room S (originally scheduled for today, in celebration of Pi Day) has been postponed because of a meeting. Because there are also meetings Tuesday, Wednesday, and Thursday after school, rescheduling may be difficult. However, stay tuned for more information.

 

T 3/15/05

HW due: §7.4 #1, 5, 6, 21, 24, and the supplementary problem described below. For each problem, show a sketch, your integral setup, and the calculator answer correct to 3 decimal places. Do not attempt to use FTC1.

Supplementary problem (not in book): Consider the space curve defined parametrically as follows:

x = 4 cos t
y = 4 sin t
z = t

(a) Sketch the curve (very roughly) for t values from 0 to 6
p.
(b) The curve is called a helix. What real-world shape does it resemble?
(c) Calculate the length of the curve for t values from 0 to 2
p, inclusive.
(d) A circle of radius 4 (which is what the xy-plane parametric curve is tracing) has a length of 2
pr = 8p. Explain why your answer to part (c) is larger than this.

 

W 3/16/05

HW due: Read the statistics portion of §7.5 (toward the end of the section), and attempt as much of the quiz as you can. You may wish to consult with a STAtistics student—that would actually be helpful review for them, since the AP Statistics exam is coming up in May.

 

Th 3/17/05

HW due: Repeat yesterday’s quiz with the knowledge you now have. Try to get all of the problems correct. You may wish to print out a clean copy for yourself.

Hints: You will find the formula z = (x
m)/s to be helpful in solving some of the problems; m denotes mean, and s denotes standard deviation. Also, when you are trying to find the z score that corresponds to a certain area, you can either try repeated guess-and-check with normalcdf, or if you grow tired of that, you can use the invNorm function under your calculator’s DISTR menu. For example, invNorm(.2) » –0.8416, which means that the z score associated with the first quintile of a normal distribution is approximately –0.8416.

In class: Discussion of the links between statistics, calculus, and precalculus.

 

F 3/18/05

Last day of class before spring break. HW due: Finish reading §7.5 if you have not already done so (including reading notes). Juniors are exempt from this requirement. No written HW for anybody.

 

Week of 3/21/05

Spring break.

 

Week of 3/28/05

Spring break.

 

 


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Last updated: 24 May 2005