Welcome to Physics 50

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Welcome to Physics 50 !
Section 1 MWF 830 Section 2 MWF 930

• Dr. Monika Kress
• Sci 262
• mkress _at_ science.sjsu.edu

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Physics is the study of the natural laws that
govern matter and energy
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engineering
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Online homeworkCourse ID is MKRESS50
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Have you taken physics in high school or college?

• Yes
• No

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Uncertainty, error, accuracy, significant digits
How many significant digits? 3.450

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• 2
• 3
• 4
• 5
• 6

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How many significant digits? 4.0 x 10-03

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• 2
• 3
• 4
• 5
• 6

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How many significant digits? 0.00020

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• 2
• 3
• 4
• 5
• 6

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• Todays class
• Review significant digits
• Units and unit conversion
• Vectors and scalars
• Addng vectors
• Vector multplication

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• 14 x 10.0
• 140.
• 140
• 140.0
• 100

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0.01 0.006 _______

• 0.01
• 0.02
• 0.016
• 0.0160

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• 4.00x10-4 6.0x10-5
• 4.600x10-4
• 4.6x10-4
• 4.60x10-4
• 5x10-4

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• 4x10-4 6x10-5
• 4.600x10-4
• 4.6x10-4
• 4.60x10-4
• 5x10-4

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• 4.00x10-4 1.0x10-2
• 1.0400x10-2
• 1.04x10-2
• 1.0x10-2
• 1x10-2

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Units and unit conversions
How many seconds in one year?
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Equations vs. units
In equations,

• Mass is always m (sometimes M )
• Time is always t
• Length can show up as l, r, d, s, x, y, z,
  depending on the situation

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• SI (mks) unit for
• Mass (m) is the kilogram, kg
• Time (t) is the second, s
• Length (l, r, d, s) is the meter, m
• All other units are combinations of these three.

What are the units of G, the gravitational
constant?
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How many square meters in 1 square km?

• 102
• 103
• 104
• 105
• 106

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scalars vectors Distance displacement Speed
velocity
Vectors have a magnitude and direction
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Adding vectors graphically

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Adding vectors numericallyStep1 resolve the
vectors into components
Given B is 3 m??? B??270o
Given A is 6 m, ?A??55o
Ax A cos?A Ay A sin?A
Components are not vectors!!!
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Adding vectors numericallyStep2 add up all the
x components Then add up all the y components
? B??270o
Given A is 6 m, B is 3 m, and angles
Bx 0
By
By -3
Ax Bx Cx
Ay By Cy
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Find ?C?
Cy 1.91
?C?
Cx 3.44
?C? arctan(Cy/Cx)
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There are two ways to multiply vectors
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Homework problem draw in vector components
Angle is always that made by the hypotenuse and
the adjacent
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How the HW deals with significant digits.
I entered 7.278
The purple box does not mean you did anything
wrong! It gives helpful info for the rest of the
problem.
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Sometimes you get the purple box even when you
entered exactly what they wanted.
Conclusion look at the purple box. Sometimes it
is useful.
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