Assignment 21 25

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course Mth 158

7/1 930

If your solution to stated problem does not match the given solution, you should self-critique per instructions at http://vhcc2.vhcc.edu/dsmith/geninfo/labrynth_created_fall_05/levl1_22/levl2_81/file3_259.htm.Your solution, attempt at solution:

If you are unable to attempt a solution, give a phrase-by-phrase interpretation of the problem along with a statement of what you do or do not understand about it. This response should be given, based on the work you did in completing the assignment, before you look at the given solution.

021. `* 21

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Question: * 2.5.8 / 2.7.8 (was 2.6.6). y inv with sqrt(x), y = 4 when x = 9.

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Your solution:

y= k/ sqrt(x)

4= k / sqrt(9)

4=k / 3

4 * 3 =12

So the equation would be:

y= 12 / sqrt(x)

confidence rating #$&*: 3

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Given Solution:

* * The inverse proportionality to the square root gives us y = k / sqrt(x).

y = 4 when x = 9 gives us

4 = k / sqrt(9) or

4 = k / 3 so that

k = 4 * 3 = 12.

The equation is therefore

y = 12 / sqrt(x). **

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Self-critique (if necessary):

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Self-critique Rating: 3

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Question: * 2.5.12 / 2.7.12 (was 2.6.10). z directly with sum of cube of x and square of y; z=1 and x=2 and y=3.

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Your solution:

z=(x^3 + y^2)k

1=(2^3 + 3^2) k

1=17K

K=1/17

The equation then is

Z=(x^3 + y^2) / 1/17

confidence rating #$&*: 2

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Given Solution:

* * The proportionality is

z = k (x^3 + y^2).

If x = 2, y = 3 and z = 1 we have

1 = k ( 2^3 + 3^2) or

17 k = 1 so that

k = 1/17.

The proportionality is therefore

z = (x^3 + y^2) / 17. **

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Self-critique (if necessary):

Why does the denominator become 17 instead of dividing it by the fraction 1/17?

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Self-critique Rating: 2

@&

The form is

z = k (x^3 + y^2)

k = 1/17.

1/17(x^3 + y^2) = (x^3 + y^2) / 17.

*@

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Question: * 2.5.20 / 2.7.20 (was 2.6.20). Period varies directly with sqrt(length), const 2 pi / sqrt(32)

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Your solution:

T=k * sqrt(L) with K= 2pi/sqrt (32)

So T= 2pi/ sqrt(32) * sqrt(L)

confidence rating #$&*: 3

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Given Solution:

* * The equation is

T = k sqrt(L), with k = 2 pi / sqrt(32). So we have

T = 2 pi / sqrt(32) * sqrt(L). **

**** What equation relates period and length? ****

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Self-critique (if necessary):

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Self-critique Rating: 3

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Question: * 2.5.42 / 2.7.42 (was 2.7.34 (was 2.6.30). Resistance dir with lgth inversely with sq of diam. 432 ft, 4 mm diam has res 1.24 ohms. **** What is the length of a wire with resistance 1.44 ohms and diameter 3 mm? Give the details of your solution.

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Your solution:

R=k * l / d^2

1.24= k * 432 / 4^2

K =1.24 * 4^2 / 432

K= 0.046

Then

R= 0.046 * L/ D^2

If D=3 and K= 0.046 Solve for L

1.44= 0.046 * L / 3^2

L= 1.44 * 3^2 / 0.046

L = 280 so the wire should be about 280 ft long.

confidence rating #$&*: 3

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Given Solution:

* * We have

R = k * L / D^2. Substituting we obtain

1.24 = k * 432 / 4^2 so that

k = 1.24 * 4^2 / 432 = .046 approx.

Thus

R = .046 * L / D^2.

Now if R = 1.44 and d = 3 we find L as follows:

First solve the equation for L to get

L = R * D^2 / (.046). Then substitute to get

L = 1.44 * 3^2 / .046 = 280 approx.

The wire should be about 280 ft long. **

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Self-critique (if necessary):

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Self-critique Rating: 3

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Self-critique (if necessary):

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Self-critique (if necessary):

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