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!

Momentum/Impulse question

  1. Nov 22, 2005 #1
    I can't seem to get past this one, and it should be possible to solve without using integration. Any help would be great :D

    A 0.25 kg object is stationary on a frictionless surface. At t = 0, a horizontal force begins to move the object. The force is given by F = (12 - 3t^2) and acts until its magnitude is zero.

    a) What is the magnitude of the impulse between t = 0.5 and t = 1.25 s?
    b) What is the change in momentum from when the object is stationary to when the magnitude of the force is zero?
     
  2. jcsd
  3. Nov 22, 2005 #2

    mezarashi

    User Avatar
    Homework Helper

    I really don't see how this one can be solved without calculus. The force is not constant, meaning the acceleration is not constant. None of the elementary kinematics equations will apply. Only the differential form of Newton's 2nd law should be used.
     
  4. Nov 22, 2005 #3

    dx

    User Avatar
    Homework Helper
    Gold Member

    Force is not constant. You have to integrate.
     
  5. Nov 22, 2005 #4
    Ok, thanks a lot. Another quick one that I am stumped on:

    A thin rod rotates around one end. Its angular acceleration is 3/2 radians / second^2 and has a rotational kinetic energy of 1.60 J at t = 4s. What is the kinetic energy at t = 0s?

    A graph was given of this question, pretty much modeling a straight line on velocity / time graph. At t = 0 the velocity looks to be about 1.4 if that helps :)
     
  6. Nov 23, 2005 #5

    andrevdh

    User Avatar
    Homework Helper

    Use the fact that that the ratio of the rotational kinetic energies at two different times are equal to the ratio of the square of the angular velocities at these times. Then by [itex]v=\omega r[/itex] the r's cancel. So you are left only with the velocities squared, which can be determined with the graph.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Momentum/Impulse question
Loading...