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!

Honors physics intermediate force question

  1. Jun 21, 2011 #1
    1. The problem statement, all variables and given/known data
    Question: An object traveling at a constant speed of 22m/s begins to experience a force of 15N in the opposite direction of its motion. (Hint given: Start by finding objects acceleration)

    a. How long will it take for the 8kg object to come to a complete stop once it experiences the force?
    b. If the object was traveling in a straight line, how far did the object travel as it slowed down?


    2. Relevant equations
    I am not exactly sure what the relevant equations are for this problem but here are the equations we have used so far in this unit.

    F=ma
    W=mg
    Fs=μsxFn (Static friction=mu times normal force)
    Fk=μkxFn (Kinetic friction=mu times normal force)

    I am guessing that I have to use one of those equations.
    3. The attempt at a solution
    Here is my small attempt.
    F=ma
    15N=(8g)(a)
    a=1.875m/s^2

    This is where I get stuck. First off I don't even know if the value I got for acceleration is correct and secondly where do I go from here. Do I go back to my kinematics equations to find time in part "a" and X in part "b"?
     
  2. jcsd
  3. Jun 21, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your acceleration is correct. And yes, time to dust off the kinematics equations to answer the questions.
     
  4. Jun 21, 2011 #3
    Would it be easier to find time (t) first or X first? And I know that the final velocity will be 0m/s but what is the initial velocity. I don't think it's 22m/s but I guess it could be...
     
  5. Jun 21, 2011 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Sure it is. That's given.
     
  6. Jun 21, 2011 #5
    I ended up getting a negative value for X...is that possible?
     
  7. Jun 21, 2011 #6

    Doc Al

    User Avatar

    Staff: Mentor

    No. Show what you did.

    Did you find the time first?
     
  8. Jun 21, 2011 #7
    No I found X first. This is what I did.
    Vfx^2=Vix^2+2aX
    0=(22^2)=2(1.875)(X)
    -484=3.75(x)
    x=-129.07

    X=Vxt
    -129.07=22(t)
    t=-5.87sec

    What did I do wrong?
     
  9. Jun 21, 2011 #8

    Doc Al

    User Avatar

    Staff: Mentor

    You have the wrong sign for the acceleration. Remember it acts opposite to the velocity, so if the velocity is positive the acceleration must be negative.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Honors physics intermediate force question
Loading...