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!

Homework Help: Creating an impact

  1. Mar 29, 2007 #1

    I am probably going to suffer some embarassment, once I see the answer to my question. Anwyay, I need to calculate the distance needed to create a 5ft-lbs. impact with a 1.18lb. sphere being dropped vertically onto a surface.

    How would I go about calucating the vertical distance needed?

    This is for an impact test from UL, where the mass and impact force are defined, but the distance is not.

    Please help a newbie. :uhh:
  2. jcsd
  3. Mar 29, 2007 #2
    (well I abhor those english units, but I reckon the principles are the same). what i like even less are words like "impact." since its in ft-lb, I assume they are looking for energy.

    there are a few ways to go about this, but usually the most direct is to equate potntial and kinetic energies

    wt*h=1/2Mv^2=impact energy
  4. Mar 30, 2007 #3
    Still unclear...

    So if the Mass of the sphere (M) = 1.18 lbs = .535kg & the impact force = 5 ft. lbs. = 6.8 Joules, then is the velocity = to acceleration by gravity ~ 9.8m/s^2?

    So it's .5(.535kg * (9.8 m/s^2)) = 6.8 Joules ??
  5. Mar 30, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper

    If your you want your final kinetic energy to be E, then use E=mgh. Or like denverdoc said, E=F*d (force times distance). Gravitational force is 1.18 lbs, you want 5 ft-lbs of impact energy, so d=E/F=(5/1.18) ft.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook