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Homework Help: Help with several problems

  1. Jan 4, 2005 #1
    I should preface this by the fact that I have yet to actually learn anything in class because today was hand out the syllabus day but I don't feel like waiting and the homework is online. I got most of them but these have given me problems. You don't need to solve them for me I'd prefer you didn't but point me in the right direction.

    The mass of the planet Saturn is 95.26 times the mass of the Earth. Saturn is very nearly spherical, with a mean radius of 5.79×107 m. Calculate the mean density of Saturn in gm/cm^3. Data: Mass Earth = 5.97 x 1024 kg.

    Let V = 5.0×10-8 c (In physics, c almost always represents the speed of light).
    Find 1 - (1 - V2/c2)1/2.

    A swimmer heads directly across a river, swimming at 2.0 m/s relative to still water. He arrives at a point 44.0 m downstream from the point directly across the river, which is 74.0 m wide. In what direction should the swimmer head so as to arrive at the point directly opposite his starting point? Express your answer in terms of the angle, in degrees, with respect to a line drawn directly across the river.

    The radius of the orbit of Pluto is about 6460.0000km. Imagine a long rope that circles the sun at just this radius. How much additional rope must be added in order to have the radius of the circle increase by just 1mm. Give your answer in units of km.

    An automobile is moving along a highway in a way that its position, as a function of time is given by X=A+Bt+Ct^2, where A=4.00m, B=-9.00m/s and C=6.00m/s^2. The automobile starts at t=0s.
    What is the magnitude of the distance from the start, in meters, when the automobile is at rest?

    Any help would be much appreciated :smile:
  2. jcsd
  3. Jan 5, 2005 #2
    self-bump self-bump
  4. Jan 5, 2005 #3


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    You just posted the problems.We're here to help you,if u have difficulties.Question:Where do you have difficulties??At each problem,only at the first,at the last two...?
    We won't do your homework.We're just gonna help,in case u get stuck.By the looks of it u haven't really started...

  5. Jan 5, 2005 #4


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    It'll be easier if you show us what you have done.
    The procedures are straightforward, so hints will be tough to give.

    1. Calculate the mass of Saturn. Find the volume of Saturn (sphere with given radius).
    Get the density from this and convert to the right units.

    2. Just enter v into the formula.

    3. You are given the speed of the swimmer relative to the water. From this you can calculate the time it takes to reach the other side and the speed of the water relative to the bank. If the swimmer wants to swm straight across he has to have a velocity component upstream to cancel out the downstream velocity of the water. Draw a diagram for this.

    4. Calculate the circumference of the given radius R and R+1mm.

    5. x(t) is given. The speed is the derivative of this. Calculate when x'(t)=v(t)=0 then use this to see what the displacement is.
  6. Jan 5, 2005 #5
    K I solved them all I was just being stupid and sloppy I kept trying to solve for the volume of Saturn as a circle not a sphere lol thanks.
  7. Feb 4, 2005 #6
    I'm having trouble solving one very similar to the 3rd one you posted regarding the river crossing....can you guys help me set that one up? I think I'm supposed to use the Vx*cos(theta) equation, but not sure....

    BTW, first post here, sup guys :)
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