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Homework Help: Car and satillite problem

  1. Sep 30, 2007 #1
    1. The problem statement, all variables and given/known data

    1. Starting from rest, a car travels 1350m in one minute. It accelerated at 1m/s2 until it reached its cruising speed. Then it drove the remaining distance at constant velocity. What was its cruising speed?

    2. A satellite is in a circular orbit 600km above the Earth’s surface. The acceleration of gravity is 8.21m/s2 at this altitude. The radius of the Earth 6400km. Determine the speed of the satellite and the time to complete of orbit around earth.

    2. Relevant equations
    problem 1:


    t1 t2
    |___________.______________________> time x
    d1 d2

    d1+d2=1350m t1+t2=60 secs

    d1=a(t1)squared d2=v(t)sqaured

    problem 2:

    v=d/t = pie*diameter/t

    3. The attempt at a solution

    problem 1:
    i derived these two formulas

    i don't know where to go from there because i have 2 unknown variables, v and t1.

    problem 2:




    i got the answer for speed and time, but i'm not sure if i did it right.
  2. jcsd
  3. Sep 30, 2007 #2
    problem 1:

    Your equation

    d = a*t1^2 + v*(t-t1)

    is correct but you're forgetting that the cruise velocity v is also constrained by being the result of acceleration for t1 time:

    v = a*t1

    so you can substitute for v into the d equation and you end up with a quadratic equation with one unknown.

    problem 2:

    Your answers seem to be correct. Btw, your math would look much more clear if you did something like "v^2" to mean "v squared".
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