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Homework Help: Basic Physics

  1. Nov 8, 2008 #1
    The diagram shows a strip of paper tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second.

    What was the speed of the object?

    A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s

    Completely clueless..

    2. If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
  2. jcsd
  3. Nov 8, 2008 #2
    1/. First you need to calculate the distance between dots. You are given the distance 10 dots covers, so this is easy. Then multiply by dots per second.

    2/. What happens to the density of water as it freezes? Surely you know the answer to that.
  4. Nov 8, 2008 #3
    Distance btw dots are 2cm, btw, do you count the first dot as zero? because I counted there are 11 dots for the 20cm.
    Also, do you mean 'divide' by dots per second instead of multiply, because I could not get the answer if I multiply it.
    1 dot = 1/50 s
    10 dot = 1/5s
    s= d/t
    s= 20/(1/5)
    Am i correct?

    The volume will decrease since the molecules are closer together, thus higher density?
  5. Nov 8, 2008 #4
    The idea is to actually count the spaces between the dots, not necessarily the dots themselves. 11 dots, 10 spaces.

    Your answer is correct, but I did mean multiply: I was actually thinking this:

    Distance between dots = 2 cm, so speed = (50 dot/sec)*(2 cm/dot) = 100 cm/sec

    2/. For most substances that would be correct, but water is different from most substances. Water actually decreases in density when you freeze it. This is why ice floats on liquid water: the ice has a smaller density than the liquid water.
  6. Nov 8, 2008 #5
    1). Seems correct to me :D
    2) What happens to a full bottle of water in the freezer?
  7. Nov 8, 2008 #6
    Thank you so much! I understand now.
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