Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Instaneous power delivered by the force at any timet

  1. Oct 16, 2004 #1
    A force F acts on a particle of mass m. The particle starts from rest at t=0.
    a) show that the instaneous power delivered by the force at any timet is (F^2/m)*t
    Please give some directions how to solve it . Thank you
     
  2. jcsd
  3. Oct 16, 2004 #2
    Any idea where to start? (hint: what is the formula for power)
     
  4. Oct 16, 2004 #3
    formula P=W/t or P=FV , and I don't know how to get t and and m involve in the formula
     
  5. Oct 17, 2004 #4
    Think of the definition of velocity. [tex]v = a t[/tex]. And then use Newton's Seond Law for [tex]a[/tex].
     
  6. Oct 17, 2004 #5
    Thank you very much, I got it, and I have another homework.
    A raindrop (m=3.35*10^-5 kg) falls vertically at a constant speed under the influence of gravity and air resistance. after the drop has fallen 100m,
    a)what is the work done by gravity?
    b)the energy discipated by air resistance?
    I got no clue for air resistance . Thank you
     
  7. Oct 17, 2004 #6
    If the raindrop where in the vacuum, the falling speed will not be constant. But when we do the experiment in a fluid, then a viscosity force appears and makes the raindrop or something else reach a constant speed. This force is proportional to the speed, so you may use newtonian physics...
     
  8. Oct 17, 2004 #7
    is it called resistive force?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook