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Homework Help: A couple of new problems

  1. Aug 25, 2005 #1
    ok this is a new subject and my teacher is just horrible, so any help will be great thanks

    1. One cubic centimeter (1.0 cm3) of water has a mass of 1.0 e-3 kg. Determine the mass of 1.0 m3 of water (in kg).
    -I thought you would take the 1.0 e-3 kg and multiply it by 100 since you are going from centimeters to meters.

    2. Assuming biological substances are 98% water, estimate the masses of a cell with a diameter of 1.3 µm, a human kidney, and a fly. Take a kidney to be roughly a sphere with a radius of 3.5 cm and a fly to be roughly a cylinder 3.7 mm long and 1.1 mm in diameter.
    -For this problem i used the conversion factors where 1.3 µm equals 1e-6 meters, and 3.5cm equals .0035 meters, and 1.1 mm equals .00011 meters and then used the volume formulas for each shape...

    3.A driver in a car traveling at a speed of 60 mi/h sees a deer 100 m away on the road. Calculate the minimum constant acceleration that is necessary for the car to stop without hitting the deer (assuming that the deer does not move in the meantime).
    -I first converted the mph to m/s since that is how acceleration is expressed and then i got stuck...

    4.A car starts from rest and travels for 10.0 s with a uniform acceleration of +1.8 m/s2. The driver then applies the brakes, causing a uniform acceleration of -1.0 m/s2. If the brakes are applied for 1.0 s, How far has it gone?
    -I am not sure where to go when looking for displacement in this situation

    5.A ball is thrown vertically upward with a speed of 11.0 m/s,
    (a) How high does it rise
    (b) How long does it take to reach its highest point
    (c) How long does the ball take to hit the ground after it reaches its highest point
    (d) What is its velocity when it returns to the level from which it started?
    -I started the class late and never recieved any formulas for questions such as these...

    6.A ball is thrown upward from the ground with an initial speed of 30 m/s; at the same instant, another ball is dropped from a building 5 m high. After how long will the balls be at the same height
    -same for this one...

    7. Two people are pulling a objest with separate ropes, one (F1) at an angle of 75 with magnitude 130 and the other (F2) at angle 60 and magnitude 80
    (a)Find the single force that is equivalent to the two forces shown, direction and magnitude
    (b)Find the force that a third person would have to exert on the mule to make the net force equal to zero, direction and magnitude
    - I only know how to do this when they are back to front vectors

    8. brick is thrown upward from the top of a building at an angle of 25° to the horizontal and with an initial speed of 10 m/s. If the brick is in flight for 3.1 s, how tall is the building?
    -dont know where to begin

    9.A jet airliner moving initially at 300 mi/h due east enters a region where the wind is blowing at 110 mi/h in a direction 25.0° north of east. What is the new velocity of the aircraft relative to the ground?
    -dont know where to begin

    -I know there is a lot, but i just dont understand these problems, ANY help will be greatly appreciated, Thanks
  2. jcsd
  3. Aug 25, 2005 #2


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    Science Advisor

    Your teacher is "horrible"? Meaning, I presume, that you can't be bothered to actually pay attention to him!

    No, because no one said anything about meters. How may cubic meterse there in 1.0 m3?

    You have a serious problem with the difference between linear measures and measures of area or volume, don't you?

    Was it the arithmetic that cause the problem? You know that x= (1/2)at2+ v0t+ x0 don't you?
  4. Aug 25, 2005 #3


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    Homework Helper

    you'd better try to talk with your teacher ...
    if you think a "couple" problems is 9!

    You should get help with vector components ASAP,
    the algebra functions can wait till next week.

    3.5 cm = 35 mm = 35e-3 m (don't let the cm throw you)
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