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Math Help - Help me solve this problem ive been having trouble.

  1. #1
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    Help me solve this problem ive been having trouble.

    First Problem.

    The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.


    Ive been having trouble doing this problem. I know that the formula is F=kws2
    r
    the r goes under kws2

    i need help solving this.
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  2. #2
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    Quote Originally Posted by Weezergames View Post
    First Problem.

    The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.


    Ive been having trouble doing this problem. I know that the formula is F=kws2
    r
    the r goes under kws2

    i need help solving this.
    Think about the facts you've been given.

    F varies inversely with the curvature, r. F varies directly with the square of the speed, s. F varies directly with the weight of the car, w.

    So your formula should look like this:

     F = K\frac{s^2 w}{r}

    Where k is a constant of proportionality. You need to find k, but luckily, you know that the force required to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft is 266lb. So if you plug these into the equation, you can solve for k. Then you will have a relation. From there, just plug in the numbers from the problem you don't know F for, and solve for F.
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  3. #3
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    Talking

    Please review this other posting of the same exercise.
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  4. #4
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    Whoa. You're going to have to rewrite this:

    The Force needed to keep a car from skidding on a curve vasies directly as teh weight of the car and the square of the and inversely as the radius of the curve. It requiers 266lb of force to keep a 2200 lb car traveling at 30 mph from skidding on a curve of radius 500 ft. How much force is required to keep a 3000lb car traveling at 45 mph from skidding on a curve of radius 400 ft.
    F=\frac{kws^{2}}{r} yes? Then:

    F is force.
    k is a constant.
    w is the weight of the car
    s is velocity.

    Yes? On the first part of the problem we know that:

    F=226lb/ft (not just lb's)
    w=2200lb
    s=30m/hr (converted into ft/s)
    r=500ft

    What don't we know. We don't know "k". We can solve:

    226(lb/ft)=\frac{k(2200lbs)(30*5280ft/s)^{2}}{500ft} for k yes? I kept the units so you can see how we got lb/ft.

    Then it's simply a matter of placing k back into our original equation, and solving a new one.
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