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1018

  • one year ago

(physics) You drive on Interstate 10 from San Antonio to Houston, half the time at 79 km/h and the other half at 105 km/h. On the way back you travel half the distance at 79 km/h and the other half at 105 km/h. What is your average speed (a) from San Antonio to Houston, (b) from Houston back to San Antonio, and (c) for the entire trip? (d) What is your average velocity for the entire trip?

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  1. 1018
    • one year ago
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    my answer for (a) is (79+105)/2 = 92 and (d)= 0. are these correct?

  2. anonymous
    • one year ago
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    Yes.

  3. 1018
    • one year ago
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    thanks. but how do i solve for b and c?

  4. anonymous
    • one year ago
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    b) is done exactly the same way as a). What do you think?

  5. 1018
    • one year ago
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    yeah, that's what i thought. that it would be tha same but it was wrong when i tried it.

  6. 1018
    • one year ago
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    i also found a similar question with different values, and they a and b werent the same either

  7. anonymous
    • one year ago
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    Can't understand why. Half the trip is at 79 and the other half is at 105.

  8. 1018
    • one year ago
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    i know! me neither

  9. 1018
    • one year ago
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    and c would be just a+b / 2 it was also wrong

  10. anonymous
    • one year ago
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    Oh, I get it now. The difference is, for the return trip, half the DISTANCE is at 79 and the other at 105. Gotta read carefully.

  11. 1018
    • one year ago
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    OOOH I didnt see that hahaha

  12. 1018
    • one year ago
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    wait ill try haha. can you answer it too? just to see if im right

  13. anonymous
    • one year ago
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    Sure. Go ahead.

  14. anonymous
    • one year ago
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    for 2nd consider the the distance between the 2 places be \[s=2x\] Assume time taken \[t_{1}\] for first half of the distance and time \[t_{2}\] for the 2nd half \[v_{av}=\frac{s}{t}=\frac{s}{t_{1}+t_{2}}\] Let us find t1 and t2, \[t_{1}=\frac{s/2}{79}=\frac{x}{79}\] similarly \[t_{2}=\frac{x}{105}\]\[v_{av}=\frac{2x}{\frac{x}{79}+\frac{x}{105}}\] On simplification the x will be cancelled, alternatively you could do this with just the s and without introducing the x

  15. 1018
    • one year ago
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    i got 90? is that correct? @Nishant_Garg

  16. anonymous
    • one year ago
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    that's a good enough answer, it will not come as a round figure, I'm getting around 89.19

  17. 1018
    • one year ago
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    is it ok? originally i got 90.12 something. was that wrong or that's acceptable already?

  18. 1018
    • one year ago
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    oh nevermind, 90 was correct. haha. thanks!

  19. anonymous
    • one year ago
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    for 3rd I assume you take the average of the forward and back trip's speed's

  20. 1018
    • one year ago
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    yes that's what i did, and it's correct

  21. anonymous
    • one year ago
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    actually yeah, I made a slight mistake 90.16 is the correct answer so approximately 90

  22. anonymous
    • one year ago
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    for the 2nd part

  23. anonymous
    • one year ago
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    so for 3rd it should average of 90 and 92, so 91

  24. 1018
    • one year ago
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    yes, all answers were right. thanks!

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