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: Rotational Motion FInding the total ENergy

  1. Aug 12, 2004 #1
    ball has a radius of 2.5 cm a mass of .125 and is rolling across a table with a speed of .547 m/s, this table is 1.04 m off the ground. It rolls to the edge and down a ramp How fast will it be rolling across the floor?

    First I found the Gravitational Potential Energy: Ep=mgh
    Initial of 1.2753 FInal = 0

    THen the Linear Kinetic ENergy : 1/2 mv^2
    Initial .0187005625 FInal .0625v^2

    Elastic Potential Energy: .5k(delta)x^2
    0 0

    Rotational Kinetic Energy: 1/5mv^2
    initial .007480225 FInal .025v^2

    Now I need to bring them all togther and solve the final velocity.

    Is the Sum of the inital energy's = to the SUM of the final energy's?
    If that's true then 1.30148075 = .0875v^2
    so v = 3.85 m/s
    Is that at all right??
  2. jcsd
  3. Aug 12, 2004 #2
    I need help ASAP

    Is anyone out there????

    I would appreciate the help :confused:
  4. Aug 13, 2004 #3


    User Avatar
    Science Advisor
    Homework Helper

    Looks ok to me. (I got 3.86 m/s, by rounding off)
  5. Aug 13, 2004 #4

    Doc Al

    User Avatar

    Staff: Mentor

    rotational KE

    I didn't check your arithmetic, but I have some comments.
    The rotational KE is [itex]{KE}_{rot} = 1/2 I \omega^2[/itex].

    You will also need the "rolling condition": [itex]V = \omega R[/itex].
    Yes, if you assume energy is conserved, which seems reasonable for this problem.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook