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PHYS 2108 Study Guide - Final Guide: Relative Change And Difference, Linear Density, Inclinometer

Course Code
PHYS 2108
Study Guide

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oHow many significant digits are in this number? 0.00001980. 4
oTwo graduate students measure the strength of an MRI’s magnetic field to have
the following values:
Student A: 8.10 +/- 0.09 T
Student B: 8.04 +/- 0.05 T
Do the two students agree for the strength of the magnetic field? Yes
oIf I want to compare values before and after an event, I would use: percent
oIf I want to compare two separate values, I would use: percent difference
oIf I want to compare predicted results to my measure results, I would use: percent
oDoes setting up a best fit line mean “connecting the dots”? No
oSuppose we want to linearize by substitution the formula for dependent variable
Kinetic Energy (K) with independent variable velocity (v). if the original equation
is K= (1/2)mv2, what will our “new” independent variable (x) be when we “map”
this onto y=mx + b? v2
oYou perform an experiment in slacking off at work by clocking out earlier each
week and seeing how it affects your paycheck. Properly title the graph and label
the axes for the plot your collected data.
Title: pay received vs. time worked
Y: pay received ($)
X: time worked (hours)
oThe known area of a table is 1.50 m2. You measure the length of the table to be
1.25 m and the width to be 1.25 m. what is the percent error between the known
area of the table and the measured area of the table you calculate using A=L*W?
percent error: measured area – known area/known area * 100
measured area: 1.25 * 1.25
oMomentum is defined as mass times velocity. You find the mass of a car to be
2077.48 kg and the velocity of the car to be 6.9 m/s, giving you a momentum of
14334.612 kg-m/s. round this momentum to the correct number of significant
digits. 14000
Due to 6.9 m/s only being 2 significant figures.
oOne example of tolerance “that matters in the real world” can be found in
radiation oncology clinics. Physicians will prescribe some dose of radiation to a
patient’s tumor that must be delivered within a certain tolerance (or range of
doses) in order to control the tumor. If a physician prescribes 52.9 Gy +/- 2.00%,
what is the maximum dose the patient can receive (in Gy)? Note: A Gy is measure
of the amount of energy deposited per unit mass.
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oHumans live an average of 79.8 years in the US. Express this time in units of days
if the conversion factor is exactly 365.25 days. Round your answer to the correct
number of significant digits as given by the original time in years.
29100 days
365 days in a year  365*79.8 = 29127, sig figs29100
oThe speed of light is 299,792,458 m/s. however, most physicists round this
number to 3x108 m/s. what is the percent difference in these values using the
correct number of sig figs? Assume the exact speed of the light is the reference
0.07 %
percent difference: rounded # - actual #/rounded # * 100.
oWhich of the following instruments will you be using to make measurements this
week in lab? Triple beam balance, meter stick, and digital caliper.
oIn MKS units, final answers of time should always be given in which of the
following units? Seconds
oIn this lab (and others) we will be doing calculations with the gravitational
constant g= 9.8 m/s2. Because we will treat it as a mathematical constant assumed
to be known exactly, how many significant digits does it contain? Infinite digits
of precision and infinite significant digits.
What is the least-count of the ruler? 0.1 cm
From the picture, what is the measured value (use the correct number of
significant digits and interpolate if necessary)? 10.5 cm
The picture represents low accuracy and low precision
oYou measure a sheet of paper. The width is 8.46 inches and the length is 11.29
inches. What is the area of the paper in MKS units (m2)?
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Multiply the W and the L by 2.54 cm (conversion factor for m) and
then multiply them together, divide by 1000 to get m2
oIf gas cost $2.16 per gallon, and it takes 21 seconds to pump one gallon of gas,
how long will it take to pump $28.59 worth of gas (in seconds)? 287
$28.59 * (1/2.16) * (gallon/dollars) * (21/1) * (seconds/gallon) = 287
oYour friend weighs 147.9 lbs. what is your friends mass in MKS units (kg)?
Assume g= 9.8 m/s2 and 1 lb. = 4.448 N and that both of these conversion factors
are known exactly (for sig figs). 67
1 lb. = 0.45359237 kg… multiply by this number to get 67.
oWhich of the following are valid reasons to take multiple measurements?
You generally gain accuracy
You generally end up with a result closer to the true value.
oYou measure the masses of five bricks to be: {3.2 kg, 3.5 kg, 3.4 kg, 3.8 kg, 5.5
kg}. What is the mean and standard deviation?
Mean: 3.9, add them all together and divide by 5.
Standard deviation: 0.93
Find variances for all by: n1-mean = #, (#)2 = difference of
squares. Do this for all 5.
Add all 5 differences together (sum of squares)
Variance= sum of squares/5 = #2
SD= (variance)1/2 = answer
oYou measured the length, diameter and mass of two different cylinders. In both
cases, you found that the length had 3 significant figures and that length was the
measurement with the fewest number of significant digits. If you found the weight
densities to be 38115 N/m3 and 38084 N/m3 and you round these values to the
correct number of significant figures, can you conclude the two cylinders are
made of the same material (do they have the same weight density)? Yes
oWhat instruments will you use this week? Slotted masses, mass hanger pans,
pulleys, and force tables
oVectors have: magnitude and direction
oBreak this vector into x and y components. Keep 5 decimal places of precision.
V= 15N, = 30.
Vx= 12.990 N, Vy= 7.5000 N
Cos and sin
oFind the magnitude and direction of a vector with the following x and y
components. Keep a few digits for the result to make sense, but not too many that
we-re overconfident.
Vx = 25 N
Vy = 15 N
Magnitude: sq. root (vx2 + vy2) … 29.15 N
Direction: tan-1 (25/15) = 30.96 from the +x axis.
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