1. Not finding help here? Sign up for a free 30min 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!

Calculate the maximum height of ball 1

  1. Dec 21, 2008 #1
    1. The problem statement, all variables and given/known data
    Two balls are connected by a string that stretches over a massless, frictionless pulley. Ball 1 has a mass of 0.45 kg and is held 0.74 m above the ground. Ball 2 has a mass of 5.7 kg and is held 0.88 m above the ground. When the balls are released, ball 2 falls to the ground, looses 30 % of its kinetic energy and rebounds to some maximum rebound height. When the balls are released, ball 1 travels to some maximum height before starting to fall. Assume that ball 1 reaches its maximum height during ball 2's rebound so that the string doesn't pull.
    Calculate the maximum height of ball 1 from and ground and the rebound height of ball 2.

    2. Relevant equations



    3. The attempt at a solution
    can you check my work i am stuck
    I would calculate the kinetic energy of ball 2 just before and after it hits the ground, using
    Just before impact, ball 2 (M) and ball 1 (m) have acquired kinetic energy
    (1/2)mV^2 + (1/2)MV^2
    = M g*0.74 - m g*0.74 Solve for V of both balls, and the kinetic energy of ball 2.

    (1/2)(m + M)V^2 = 0.74 (M-m)g
    V^2 = [(M-m)/(M+m)]g*1.48 = 12.38 m^2/s^2
    V = 3.52 m/s

    = After impact, ball 2 will have 70% of the pre-impact kinetic energy, and its velocity will be V' = sqrt(0.7)V= 0.8367V = 2.94 m/s
    Right after ball 2's impact, Ball 1 will continue to rise for a while because it suffered no impact and maintained its velocity V when ball 2 hits the ground. There will be no tension in the string while ball 2 and ba1l 1 both rise.
    Ball 1 rises a distance H1 given by
    M g H1 = (1/2) M V'^2 = (1/2)M(0.7)V^2
    H1 = (0.7)V^2/(2g) = 0.35 V^2/g

    When ball 1 hits the ground, ball 2 has already risen from 0.74 to 0.74 + 0.88 = 1.62 m above the ground. It will rise an additional distance until its kinetic energy (1/2) mV^2(at impact)is converted to potential energy
     
  2. jcsd
  3. Dec 22, 2008 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi myoplex11! :smile:

    Looks good down to …
    … where you should still be using V = 3.52 (not 0.7V) :wink:

    (are you mixing up ball 1 and 2?)

    Apart from that, everything's fine.

    What are you getting for the maximum and rebound heights? :smile:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Calculate the maximum height of ball 1
Loading...