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Homework Help: Application of Newtons' Law

  1. Oct 15, 2007 #1
    (1) What is the magnitude of the net force on a skydiver in N when an 810 N gravitational force and a 750N force of air resistance act on him?

    Fn = 810
    Fg = 750

    810 - 750 = Fm


    (2) A 1200 kg car is moving in a staright line at a constant speed of 15m/s when the brakes are applied. The coefficeient of friction between the car and the road is 0.25. How far in m does the car travel after the brakes are applied?

    Fn = 1200*9.8

    F = u*Fn = 2940N

    -F = m*a

    a = -F/m = -2940/1200 = -2.45m/s^2

    Vf^2 = Vi^2 +2a*deltaX

    0 = Vi^2 +2adeltaX

    -Vi^2/2a = deltaX = -15^2/-2.45 = 45.92m

    4.) A car moves in a circle of 30 m radius. It moves with constant speed and makes one complete revolution in 22s. What is its speed in m/s?

    A = V^2/r

    that's all I have for this problem..

    can you guys help me out with this?

    Also, are my answers for 1 and 2 correct?
  2. jcsd
  3. Oct 15, 2007 #2

    Chi Meson

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    1 & 2 are good.

    Notice that you do not need to know the mass for the problem in 2. If friction is only force (and therefore the net force) on an object, and it is sliding on a horizontal surface, notice that the acceleration is always [tex] \mu g[/tex]

    for #3 you are making it too hard. speed is what over what?

    In one full circle, the distance traveled is known as the __________ .
    Last edited: Oct 15, 2007
  4. Oct 15, 2007 #3
    What about 3, sir. Any advice how to start it?
  5. Oct 15, 2007 #4

    Chi Meson

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    check previous post. I added it late.
  6. Oct 15, 2007 #5
    nevermind..I think i got it..I think it's just circumference over time..so 60pi/22
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