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Calculate time given distance, mass, and force

  1. Jul 3, 2017 #1
    << New member has been reminded by the Mentors to post schoolwork type questions in the Homework Help forums and to use the HH Template >>

    Is there any equation to find the time taken for an object to travel a certain distance if I am given the distance the object traveled, the mass of the object, and a constant force that was used to pull the object? For example, if an object with a mass of 1 kg travels a distance of 100 meters with a constant force of 9.81 newtons without stopping, is there a way to calculate the time it took the object to travel the distance of 100 meters?
     
    Last edited by a moderator: Jul 3, 2017
  2. jcsd
  3. Jul 3, 2017 #2

    berkeman

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    Welcome to the PF.:smile:

    Yes, there are equations to help you do that. Are you familiar with the kinematic equations for a constant acceleration?

    http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

    Click on Mechanics, and then Velocity and Acceleration, and then Constant Acceleration to see the equations...
     
  4. Jul 3, 2017 #3
    @berkeman Thanks, I know about kinematic equations. But currently, I don't have the velocity or the acceleration. All I have is the constant force used to pull the object, the distance it traveled, and the mass of the object.
     
  5. Jul 3, 2017 #4

    berkeman

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    Force and mass give you the acceleration. Acceleration, velocity and distance are related by the equations show in the link. Makes sense?
     
  6. Jul 3, 2017 #5
    Oh yeah! Okay. Thank you so much. Are there any other formulas other than f = ma and then finding time.
    @berkeman
     
  7. Jul 3, 2017 #6

    berkeman

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    I think for your problem, F=ma and those kinematic equations should work. Give it a try and post your work here for us to check.
     
  8. Jul 3, 2017 #7
    F = 100 N
    m = 1 kg
    a = ?
    d = 5 km
    a = 100/1 = 100 m/s
    a = 2d/t²
    100 m/s = 2(5000)/t²
    t = 10 s
    @berkeman
     
  9. Jul 3, 2017 #8
  10. Jul 3, 2017 #9

    berkeman

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    Close, but let's fix up the units. It's good that you are starting to get into the habit of carrying units along in the calculation (helps to find errors and inconsistencies)...

    F = 100 N
    m = 1 kg
    a = ? m/s^2
    d = 5 km = 5000 m
    a = 100 N/1 kg = 100 m/s^2
    d = 1/2 a*t^2 (with Vo=0), so a = 2d/t²
    100 m/s^2 = 2(5000 m)/t²
    t = SQRT(10000 m / 100 m/s^2) = SQRT(100 s^2)
    t = 10 s

    Looks pretty eGenuine to me! :smile:
     
  11. Jul 3, 2017 #10

    berkeman

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    BTW, it's good to learn the fundamental units behind quantities like Newtons to help you with the equations. For example, 1 N = 1 kg*m/s^2
     
  12. Jul 3, 2017 #11
    @berkeman Last question: Can you pull a 1 kg object with 5 N force or do you need 10 N to pull it across the floor?
     
    Last edited by a moderator: Jul 3, 2017
  13. Jul 3, 2017 #12

    berkeman

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    Beats me. F=ma and the force needed to move the object depends on the resisting force of static friction, which depends on the coefficient of friction and the objects mass. Have you studied those concepts yet? :smile:
     
  14. Jul 3, 2017 #13
    @berkeman Hey! I was creating a force vs acceleration graph. acceleration is on the x axis and force is on the y-axis. I got the slope and it was equal to the mass of the object. However, I got a y-intercept equal to 7.74. What does this represent. Is this the friction or...?
     
  15. Jul 3, 2017 #14

    berkeman

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    Usually you would put the independent variable on the x-axis, and the dependent variable on the y-axis. The input on the x-axis causes the effect on the y-axis.

    So switch axes and please post your plot. It's hard to understand what you are asking so far.

    BTW, it's great that you are asking fundamental physics questions to understand and learn. Are you in school right now (or in the FalI guess)?
     
  16. Jul 3, 2017 #15
    @berkeman I have measured the acceleration of an object already and I have found the force being applied on the same object. I have plotted this data on a graph and I have used a line of best fit to connect all the points. My slope has given me the mass of the object. However, my y-intercept seems very unusual. I expected it to be negative as I thought it might represent friction but Im getting positive 7.74 as the y-intercept value. Please explain if this is error in my data or am I interpreting this incorretly. Thank you.
     
  17. Jul 3, 2017 #16
    And no I'm not in school right now. I was just trying to solve some physics problems that I found on the internet. Was interested and decided to do some of them :)
     
  18. Jul 3, 2017 #17
    BTW, just to confirm The problem tells me to graph acceleration on the x-axis and force on the y
     
  19. Jul 3, 2017 #18

    berkeman

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    All schoolwork-type questions should be posted in the Homework Help forums, so I'll move this thread there now.

    And we need to see a sketch of your setup and see your graph to be able to help.
     
  20. Jul 3, 2017 #19
    I think this is all you need.
     

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