1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Arrow Loses Mechanical Energy

  1. Nov 13, 2016 #1
    1. The problem statement, all variables and given/known data
    A 125 - G arrow is shot vertically upwards with a Vi of 28/ms. Assuming a 20% loss in Mechanical Energy while ascending, what maximum height above the position it was shot does it reach?

    2. Relevant equations
    Vi= 28m/s
    Vf= O m/s
    D= ?
    a= -9.8 m/s

    Vf^2= Vi^2 + 2aD
    Eg = mgh
    Ek = 1/2mv^2
    EM = Eg + Ek (not sure}
    3. The attempt at a solution
    I did not really understand this question but I tried to make a solution using what I know.
    I tried using one of the 5 equations but that did not help so i tried using work and energy equations.

    So i did Ek first
    Ek= 1/2 mv ^2
    Ek = 1/2 (0.125 kg) (28 m/s)^2
    Ek = 98 J

    Next I tried finding the Eg
    Eg = Ek x 0.70
    (30% loss of mechanical energy, this is what i am thinking)
    Eg = 68.6 J

    Eg = mgh
    Eg= 0.125 (9.8) h
    68.6 = 1.225 h
    68.6/1.225= h
    h= 55.51 m

    Did I do this question right or wrong? I am very confused. Some help would be appreciated!
     
  2. jcsd
  3. Nov 13, 2016 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Where does the 30% come from? Your method is correct.
     
  4. Nov 13, 2016 #3

    gneill

    User Avatar

    Staff: Mentor

    Check that calculation. Did you divide by two?
     
  5. Nov 13, 2016 #4

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Yes it's the right approach just check the working as others have suggested.
     
  6. Nov 13, 2016 #5
    i meant 30%
     
    Last edited: Nov 13, 2016
  7. Nov 13, 2016 #6
    (In the post i meant 30% loss, not 20 % thats why i did multiplying by 0.7.)
    I divided by two so the number is 49 J , multiplying it by 0.7 would be 34.3 J
    34.3 J / 1.225 = h
    H= 28 M exactly
    Is this method now correct?
     
  8. Nov 13, 2016 #7

    gneill

    User Avatar

    Staff: Mentor

    Yes. Although "exactly" depends upon your choice of value for g :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Arrow Loses Mechanical Energy
  1. Losing energy (Replies: 3)

Loading...