



Section summary
 Time is measured in terms of change, and its SI unit is the second (s). Elapsed time for an event is
$\mathrm{\Delta}t={t}_{\mathrm{f}}{t}_{0},$
where
${t}_{\mathrm{f}}$ is the final time and
${t}_{0}$ is the initial time. The initial time is often taken to be zero, as if measured with a stopwatch; the elapsed time is then just
$t$ .
 Average velocity
$\stackrel{}{v}$ is defined as displacement divided by the travel time. In symbols, average velocity is
$\stackrel{}{v}=\frac{\mathrm{\Delta}x}{\mathrm{\Delta}t}=\frac{{x}_{\text{f}}{x}_{0}}{{t}_{\text{f}}{t}_{0}}\text{.}$
 The SI unit for velocity is m/s.
 Velocity is a vector and thus has a direction.
 Instantaneous velocity
$v$ is the velocity at a specific instant or the average velocity for an infinitesimal interval.
 Instantaneous speed is the magnitude of the instantaneous velocity.
 Instantaneous speed is a scalar quantity, as it has no direction specified.
 Average speed is the total distance traveled divided by the elapsed time. (Average speed is
not the magnitude of the average velocity.) Speed is a scalar quantity; it has no direction associated with it.
Conceptual questions
There is a distinction between average speed and the magnitude of average velocity. Give an example that illustrates the difference between these two quantities.
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If you divide the total distance traveled on a car trip (as determined by the odometer) by the time for the trip, are you calculating the average speed or the magnitude of the average velocity? Under what circumstances are these two quantities the same?
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Problems&Exercises
(a) Calculate Earth's average speed relative to the Sun. (b) What is its average velocity over a period of one year?
(a)
$3\text{.}\text{0}\times {\text{10}}^{4}\phantom{\rule{0.25em}{0ex}}\text{m/s}$
(b) 0 m/s
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A helicopter blade spins at exactly 100 revolutions per minute. Its tip is 5.00 m from the center of rotation. (a) Calculate the average speed of the blade tip in the helicopter's frame of reference. (b) What is its average velocity over one revolution?
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The North American and European continents are moving apart at a rate of about 3 cm/y. At this rate how long will it take them to drift 500 km farther apart than they are at present?
$2\times {\text{10}}^{7}\phantom{\rule{0.25em}{0ex}}\text{years}$
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Land west of the San Andreas fault in southern California is moving at an average velocity of about 6 cm/y northwest relative to land east of the fault. Los Angeles is west of the fault and may thus someday be at the same latitude as San Francisco, which is east of the fault. How far in the future will this occur if the displacement to be made is 590 km northwest, assuming the motion remains constant?
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On May 26, 1934, a streamlined, stainless steel diesel train called the Zephyr set the world's nonstop longdistance speed record for trains. Its run from Denver to Chicago took 13 hours, 4 minutes, 58 seconds, and was witnessed by more than a million people along the route. The total distance traveled was 1633.8 km. What was its average speed in km/h and m/s?
$\text{34}\text{.}\text{689 m/s}=\text{124}\text{.}\text{88 km/h}$
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Questions & Answers
Why does earth exert only a tiny downward pull?
what is radioactive element
an 8.0 capacitor is connected by to the terminals of 60Hz whoes rms voltage is 150v.
a.find the capacity reactance and rms to the circuit
thanks so much. i undersooth well
is the study of matter in relation to energy
Kintu
a submersible pump is dropped a borehole and hits the level of water at the bottom of the borehole 5 seconds later.determine the level of water in the borehole
power P = Work done per second W/ t. It means the more power, the stronger machine
Sphere
e.g. heart Uses 2 W per beat.
Rohit
A spherica, concave shaving mirror has a radius of curvature of 32 cm .what is the magnification of a persons face. when it is 12cm to the left of the vertex of the mirror
my name is Abu m.konnek
I am a student of a electrical engineer and I want you to help me
Abu
the magnification k = f/(fd) with focus f = R/2 =16 cm; d =12 cm
k = 16/4 =4
Sphere
what do we call velocity
Kings
A weather vane is some sort of directional arrow parallel to the ground that may rotate freely in a horizontal plane. A typical weather vane has a large crosssectional area perpendicular to the direction the arrow is pointing, like a “One Way” street sign. The purpose of the weather vane is to indicate the direction of the wind. As wind blows pa
what about the wind vane
Godfred
If a prism is fully imersed in water then the ray of light will normally dispersed or their is any difference?
the same behavior thru the prism out or in water bud abbot
Ju
If this will experimented with a hollow(vaccum) prism in water then what will be result ?
Anurag
What was the previous far point of a patient who had laser correction that reduced the power of her eye by 7.00 D, producing a normal distant vision power of 50.0 D for her?
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
A young woman with normal distant vision has a 10.0% ability to accommodate (that is, increase) the power of her eyes. What is the closest object she can see clearly?
Jaydie
In what ways does physics affect the society both positively or negatively
how can I read physics...am finding it difficult to understand...pls help
try to read several books on phy don't just rely one. some authors explain better than other.
Ju
And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
Ju
I have a exam on 12 february
the speed of something in a given direction.
Ju
Source:
OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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