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Can someone check these out please?

  1. Jun 29, 2005 #1
    Hello everyone,

    I appreciate all of the help I have recieved in the past and was hoping someone could confirm my answers to the following problems that I was unsure of.

    First question:

    The centripital force on a runner is 17 lb. If the runner weighs 175 lb, and his speed is 14 Mi/Hour, find the Radius of the curve.

    r=(175lb*20.5^2 ft/s)/17lb
    r=4326.1 Ft

    Second Question:

    A motor develops .75Kw of power at 2000 revolutions per 10 minutes. What Torque is applied to the motor shaft?

    T=750W / 20.93rad/s
    T=35.8 Nm

    Third Question

    A truck with mass 215 slugs rounds a curve of radius 53ft with a speed of 62.5 ft/s. A) what is the centripital force exerted on the truck while rounding the curve? B) How does the Centripital force change when the velocity is doubled? C) what is the new force?

    a) Fc=m * v^2 / r
    Fc=215 * 62.5^2 / 53
    Fc=15,846.1 lbs

    B) The force would be increased

    C) Fc=m * v^2 / r
    Fc=215 * 125^2 / 53
    Fc=63,384.4 lbs

    Last question:

    A pulley of diameter 14cm is driven by an electric motor to revolve 75 RPM. The pulley drives a second one of diameter 10cm. How many revolutions does the second pulley make in 1 minutes


    w2=105 RPM

    If anyone can help confirm my answers, I would greatly appreciate it!
  2. jcsd
  3. Jun 30, 2005 #2
    All you answers seem valid although I have one question. In the first problem is it the mass or the weight of the runner that is 175 lbs. A pound force is not equal to a pound mass. In fact 1 lbm * 32.2 ft/s^2 = 1lbf. So you may need to divide that 175 lbs by 32.2 to get your answer in terms of a mass. Slugs on the other hand are already a mass, 1 slug = 32.2 lbm
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