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[Early Phys. Science]: Speed Equation

  1. Jan 8, 2005 #1
    Hello everyone! This is my first time posting here, as it is also my first week in Physical Science class. :blushing:

    Yesterday our teacher was teaching us the formula to find out speed equations and Speed vs. Velocity, and I took two pages of notes. The problem? I stopped following them about half way through the first page.

    He sent us home with twenty problems and a promise of a quiz over the material on Monday, which sent me into a panic.

    Could someone please walk me through this problem, and then I can respond once I understand with a few that I do on my own for you to check? I'd really appreciate it!

    "A bicycle rider travels 60.0 kilometers in 3.5 hours. What is the cyclist's average speed?"
     
  2. jcsd
  3. Jan 8, 2005 #2

    HallsofIvy

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    That doesn't take two pages of notes! The DEFINITION of speed is "distance divided by time". What is 60.0 kilometers divided by 3.5 hours? That is, 60/3.5 and the units will be kilometers per hour.
     
  4. Jan 8, 2005 #3
    speed = distance/time
    velocity = speed and its direction

    Keep these two lines in your note book and throw that two pages away
     
  5. Jan 9, 2005 #4
    Oh, I feel so silly! That was very easy.

    So "How much time would it take for the sound of thunder to travel 1,500 meters if sound travels at the speed of 330 m/s?" is just 4.54 seconds! :D

    I just want to have this one checked to see if it's right. There's no special formula I was supposed to do, right? I just converted it with my calculator.

    You now know that there are 1,609 meters in a mile. The number of feet in a mile is 5,280 feet. Use these equalities to answer the following problems.

    My answer: 2.54 cm.

    So yeah..guess I was just looking at everything a little too hard. ;)
     
  6. Jan 9, 2005 #5

    HallsofIvy

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    Another way to look at that problem is to look at the dimensions. You are given "1500 m", you want to find time, in s, and you know 330 m/s. In order to go from m to s, you will have to "cancel" m and "multiply by" s: You need
    m(s/m)= s. Since dividing by a fraction is the same as inverting an multiplying, 1500m divided by 330 s is (1500/330)(m(s/m)= 4.5 s. (Since "1500 m" and "330 m/s" have two significant figures, I would use only two significant figures in my answer but I am being hard nosed!)

    ??? What was the question???
     
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