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: Work, power, acceleration problem

  1. Oct 13, 2011 #1
    A helicopter, starting from rest, accelerates straight up from the roof of a hospital. The lifting force does work in raising the helicopter. An 810-kg helicopter rises from rest to a speed of 7.0 m/s in a time of 3.5 s. During this time it climbs to a height of 8.2 m. What is the average power generated by the lifting force?

    M = 810 kg
    V0 = 0 m/s
    Vf = 7 m/s
    t = 3.5 s
    y = 8.2 m

    Force acting on helicopter: mg and FL (the lifting force)

    It is accelerating upward. Find acceleration, a:

    Vf = Vo + at
    a = (Vf - Vo)/t
    a = 2 m/s2

    FL - mg = ma
    FL = mg + ma
    FL = 810(9.8+2)
    FL = 9558 N

    P = FL x avg V = 9558 N x 3.5 m/s
    P = 33453 watts?
     
    Last edited: Oct 13, 2011
  2. jcsd
  3. Oct 13, 2011 #2

    gneill

    User Avatar

    Staff: Mentor

    Looks alright. You might want to express the result using the appropriate number of significant figures.
     
  4. Oct 13, 2011 #3
    Thank you so much! My quiz is tomorrow and I wasn't sure how to do this type of problem!!!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook