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!

Speed Problem (Please Help )

  1. Oct 16, 2008 #1
    Speed Problem (Please Help!!!)

    * A system of blocks is released from the rest. the speed of 10kg block just before it hits the ground the ground. The surface is frictionless.


    [​IMG]


    Attempt:

    I hv donw this way, but I am suppose to use work-kinetic enery theoreom or something to find the answer, which i hv no clue abt it.........thought u guys would help me



    first i found acceleration: a = g(M -m1sin45 - m2sin45)/(M+m1+m2) = 4.31 m2/s2

    then used vf2 = vi2 +2ax = 0 + 2(4.31)(5) = 42.23m2/s2

    and vf = 6.5m/s

    but i need get this answer by Work-Kinetic theorem or something............Please HElp

    Thanks in advacne
     
  2. jcsd
  3. Oct 16, 2008 #2

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Re: Speed Problem (Please Help!!!)

    Use conservation of energy. Write an expression for the total energy just before things start moving. Then write an expression for the total energy when the block hits the ground.
     
  4. Oct 16, 2008 #3
    Re: Speed Problem (Please Help!!!)

    our professor slightly went over it............can u please just write the expression, I can work tht out

    Thanks a lot for helping
     
  5. Oct 16, 2008 #4

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Re: Speed Problem (Please Help!!!)

    The exact equations should be in your text book. There is (gravitational) potential energy and kinetic energy to account for.
     
  6. Oct 16, 2008 #5
    Re: Speed Problem (Please Help!!!)

    but there r 3 blocks how do i add them together for the energy?

    starting: (m1+m2+m3)gh = .5(m1+m2+m3)v*v

    but I the height is not given for all the blocks......
     
  7. Oct 17, 2008 #6

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Re: Speed Problem (Please Help!!!)

    There are two problems here.

    1. The heights are all different. So you'll have to use h1, h2, and h3 for the heights of each block. Don't worry that the heights are not all given, it will work out in the end.

    2. Potential and kinetic energies are not equal to each other. Instead, you add them together, to find the total energy of the 3 blocks.
     
  8. Oct 17, 2008 #7
    Re: Speed Problem (Please Help!!!)

    Or you can simply find the acceleration of the system using newton's laws, and then calculate the final velocity using equations of motion
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Speed Problem (Please Help )
  1. Max speed please help! (Replies: 1)

Loading...