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course Phy 231
8/28 at 8:21 pm
Adapted from spiral outline: units, percent difference, etc.
Instructions:
1. Copy this document into a text editor, such as notepad.
2. Insert your answers between lines marked **** and #$&*. Do not insert anything into the lines so marked.
3. Do not eliminate anything that appears in this document. Insert as indicated, but otherwise do not make any changes to what you see here.
4. Submit a copy of your completed document using the Submit Work Form at http://vhcc2.vhcc.edu/dsmith/submit_work.htm .
Do the following calculations with fractions. This should take you 5 minutes or less: Do not use a calculator. You can do all the numerical calculations if you know the multiplication facts for single-digit numbers.
Each answer should be typed as a sequence of numbers, letters, slashes , asterisks and parentheses. If you have questions then please show some of the steps of your work, and you will ordinarily be asked to do so. For this document, however, just the answers will be sufficient. On these questions, I'll usually be able to figure out what you've done from your answers.
(1/2) * (3/4)
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3/8
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(12/5) * (25 / 21)
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Reduces to (4*5) / 7, so 20/7
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(4/3) * 3
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4
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(5/8) * 16
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10
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(5/9) / (3/4)
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5/12
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(13/25) / 2
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26/25
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12 / (2/3)
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18
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(4 / 3^2) * 3
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4/3
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(a/b) * (c/d)
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(a*c) / (b*d)
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(a/b) / (c/d)
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(a*d) / (b*c)
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(a/b) * c
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(a*c) / b
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a / (b / c)
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(a*c) / b
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(a/b) / c
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a / (b * c)
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(a / b) / b
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a / b^2
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(a / b^2) * b
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a / b
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(a / b^2) / b
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a / b^3
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Now do the following calculations:
(m / s) * s
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m
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kg * (m / s^2)
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(kg * m) / (s^2)
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(m/s^2) * s
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m/s
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(m/s^2) * m
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(m^2) / (s^2)
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(kg * m / s^2) / (m / s)
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Kg / s
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5 m * (1 km / (1000 m) )
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5m
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@& Technically, yes, since as you obviously kow 1 km is the same as 1000 m.
However if you do the calculation as stated you get .005 km.*@
80 ft * (31 cm / ft)
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2480cm
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20 dollars * (100 cents / dollar)
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20 dollars
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12 pounds * (9.8 Newtons / (2.2 pounds) )
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(12*9.8) N
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@& The 2.2 is also part of the calculation. You can't divide pounds by pounds without also dividing by 2.2.*@
Now answer the following:
Work out and show units in every step:
If F = m a, then if m = 5 kg and a = 3 m/s^2, what is the value of F?
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F = 5kg * 3 m/s^2, F = 15 (kg*m)/s^2
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If F = m a and F = 15 pounds when a = 5 feet / second^2, then what is m?
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F = 15lb * 5 ft/s^2, F = 75 (ft. *lb) / s^2
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@& Nothing in this question asks or implies that you multiply F by a.*@
If KE = 1/2 m v^2 with m = 2 kg and v = 4 m/s, then what is KE?
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16 (kg*m)/s
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@& Numbers are right, units aren't.
Hint: What do you get when you square 4 m/s?*@
If F = k Q q / r^2 with k = 9 GigaNewton m^2 / C^2, Q = 2 C and q = 3 C with r = 10 m, then what is F?
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27/50 (GNm^2) / C^2
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@& You didn't work the entire calculation out, step by step, but the units, and your result is not correct.*@
@& Not bad, but not complete correct. An engineer needs to be completely correct with calculations of this nature. *@
@& Check my notes.*@