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Homework Help: How to find net force using mass, distance, and time?

  1. Nov 4, 2009 #1
    1. The problem statement, all variables and given/known data[/B]
    A 2.0 kg otter starts from rest at the top of a muddy incline 85 cm long and slides down to the bottom in 0.50 s. What net force acts on the otter along the incline?

    mass = 2.0 kg
    distance = 85 cm
    time = .50 s
    net force = ?

    2. Relevant equations

    I also used.

    3. The attempt at a solution

    170/.5=340 cm/s^2
    340 cm/s^2 = 3.4 m/s^2

    (2.0 kg)(3.4 m/s^2)= 6.8 N

    The book says the right answer is 14 N though.
  2. jcsd
  3. Nov 4, 2009 #2
    No, velocity is not constant. It changes over time. You should read your textbook again or check this http://en.wikipedia.org/wiki/Equation_of_motion" [Broken] to find appropriate formula.
    Last edited by a moderator: May 4, 2017
  4. Nov 4, 2009 #3
    Hi elkosp16, you need to use the formula :

    Δ X = Vi*T + (1/2)*a*T^2

    You already know displacement (ΔX), 85 cm (remember to convert it to meters !)
    Initial velocity (Vi) is 0, because it starts at rest.
    Time = .50 seconds,
    Plug everything in and solve for a,

    once you get acceleration, use newtons second law.
    ∑ F=m*a
    plug in mass & acceleration, the answer is net force.
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