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Homework Help: Chaning Mass Kinetic Energy

  1. Apr 6, 2007 #1
    1. The problem statement, all variables and given/known data
    At a certain factory, gravels are dropped vertically from a machine at a rate of x (kg/s) onto a conveyor belt moving at velocity v.

    a. what is the force needed to keep the belt moving at velocity v?

    b. what is the power?

    c. what is the rate of change in kinetic energy?

    d. what is the difference between power and kinetic energy?

    2. Relevant equations

    F = dp/dt
    P = F (dot product) v

    3. The attempt at a solution

    I got a, b, c,

    a. F = dp/dt = dm/dt * v = x * v

    b. P = F (dot product) v = x*v^2

    c. rate of change in kinetic energy = 1/2 * dm/dt * v^2 = 1/2 *x * v^2

    d. so rate of change in kinetic energy is not same as power!!
    what is going on????
  2. jcsd
  3. Apr 6, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    Supposed I told you that dropping gravel onto a conveyor belt is an inelastic collision?
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