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How do I do this?

- Thread starter hytuoc
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- #1

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How do I do this?

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(55+90)/2 = 72.5

:)

[r.D]

- #3

Tide

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The average speed is the total distance travelled divided by the total time to make the trip.

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[r.D]

- #5

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That's the problem with the lack of a good explanation of "average velocity" in physics textbooks.DrWarezz said:

(55+90)/2 = 72.5

:)

[r.D]

"average velocity" is a

[tex]v_{av}=\frac{v_1 \Delta t_1 + v_2 \Delta t_2}{\Delta t_1+\Delta t_2}[/tex]

Only then does it logically follow that

[tex]v_{av}=\frac{\Delta x}{\Delta t}[/tex]

Generally speaking (i.e., for non-constant acceleration), the straight-average velocity has no physically interesting application.

edit:

"average speed" is a

[tex]s_{av}=\frac{|v_1 \Delta t_1| + |v_2 \Delta t_2|}{\Delta t_1+\Delta t_2}[/tex]

Only then does it logically follow that

[tex]s_{av}=\frac{d_{total}}{\Delta t}=\frac{d_{total}}{t_{total}}[/tex]

where [itex]d_{total}[/itex] is the total-distance travelled.

- #6

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Thanks robphy.

However, my solution answers the authors question, correct?

:)

[r.D]

However, my solution answers the authors question, correct?

:)

[r.D]

- #7

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Since vDrWarezz said:Thanks robphy.

However, my solution answers the authors question, correct?

:)

[r.D]

- #8

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Well, I'm guessing by the simplicity of the question, that such a method is not necessary. Instead, the teacher that set this homework :P is just wanting to see the use of averages. :) hehe.

So, to the author: If this is just some homework, and you haven't done averages at school yet (I'm assuming you're at school), then go for my answer. But, if you're, eg, at college or something, definitely go for robphys' solution :D

best of luck - and thanks for the insight robphy, I am only a young school student (15 yrs old), so, your solution is quite new to me. But, I've bookmarked it, and will surely use it in the future :D Thanks.

[r.D]

- #9

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You cannot apply the statistical definition of "average" to average speed. It is DEFINED, as stated, as the total distance travelled divided by the total time taken. Even though the total distance and time taken here are not given, this problem is still solvable if one stick to solving it symbolically in the beginning and not plug in numbers right away.DrWarezz said:

[r.D]

Zz.

P.S. This thing is posted in the wrong section of PF. We do have a Homework Help section.

- #10

Tide

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Well, you could certainly do that but consider this. Suppose you traveled at 50 km/h for the entire trip except that over the last meter you gunned it and traveled at the speed of light. Would your average speed have been half the speed of light?DrWarezz said:

[r.D]

- #11

krab

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[tex]\overline{v}={d\over t}={d\over t_1+t_2}={d\over{d\over 2v_1}+{d\over 2v_2}}={2v_1v_2\over v_1+v_2}[/tex]

- #12

Tide

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[tex]\frac {v_1 v_2}{f v_2 + (1-f)v_1}[/tex]

- #13

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[tex] \overline {v} = {v_0 + v_f \over 2} [/tex] only works if assuming constant acceleration.

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