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Homework Help: Help with physical sci problems

  1. Apr 7, 2005 #1
    Help with physical sci problems!!!

    Hey i was just wondering if any of you knew how to do these problems.... i have hw due and i dont understand these

    thanks so much!!

    1. 2 ants race across a table 67 cm long. One travels at 4.14 cm/s and the other at 3 cm/s. When the first one crosses the finish line, how far behind is the second one? Answer in units of cm.

    2.While John is traveling along a straight interstate highway, he notices that the mile marker reads 252 km. John travels until he reaches the 149 km marker and then retraces his path to the 168 km marker.
    What is Johns resultant displacement from the 252 km marker? answer in units of km
  2. jcsd
  3. Apr 7, 2005 #2
    For number 1 i get 18 cm not sure about 2nd one but i rounded down on the answerd but if you did it without rounding it is 18.449275362318 or so my calculator says. to find this you need to find how long it takes both of them to cross than figure out the difference and from there you can figure out how far behind the 2nd one is
  4. Apr 7, 2005 #3
    thank you so much!!
  5. Apr 7, 2005 #4
    so it was 18.4 cm right
  6. Apr 7, 2005 #5
    Ant 1 crosses at t = d/v = 67/4.14 = 16.18s

    Ant 2 will be at d = vt = (3)(16.18) = 48.54cm from the start line

    67cm (finish line) - 48.54 = 18.46cm behind
  7. Apr 7, 2005 #6
    For 2

    John is at 252km, he keeps going to reach 168km, so so far he has travelled:

    252km - 149km = 103km in the forward direction

    He then turns around and goes back to 168, travelling

    168 - 149 = 19km in the backward direction

    So from the 252 marker, he went 103km forwards and 19km backwards.

    +103 - 19km = 84km from the 252km marker

    Ans = 84km
  8. Apr 7, 2005 #7
    I was close just my ti-92 has to be to scientific with math
  9. Apr 7, 2005 #8
    i typed 84 into the computer because i turn in my homework online, and it said that 84 was incorrect?

    I was sure that 84 was the answer??
  10. Apr 8, 2005 #9
    Try -84? He's 84km from the 252km marker, but he travelled a total of 122km.
  11. Apr 8, 2005 #10
    oh ok, yea the next question asked for the distance which is 122.

    ill try -84
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