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Homework Help: A simple motion question ?

  1. Jan 8, 2012 #1
    1. The problem statement, all variables and given/known data
    A lorry of a mass 1500kg increases its velocity from 12m/s to 20m/s.

    2. Relevant equations
    a) calculate the change in momentum of the lorry.
    b) The time taken for this change in velocity id 2 minutes. Calculate the average resultant force applied on the lorry.

    3. The attempt at a solution
    I worked out part a) by using the formula momentum= mv and got the ans 12000kgm/s
    but i dont know how to work out part b.
    Does anyone know how ?
     
  2. jcsd
  3. Jan 8, 2012 #2

    Doc Al

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    Staff: Mentor

    Look up the impulse-momentum theorem.
     
  4. Jan 8, 2012 #3
    Thank you so the formula is that ? F⃗ Δt=Δp⃗ =m(v⃗ f−v⃗ i)
    So the Force= mass (velocity * f orce - velocity* impulse)?
     
  5. Jan 8, 2012 #4

    Doc Al

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    Staff: Mentor

    Not exactly. Impulse = FΔt. The impulse momentum theorem states that the impulse will equal the change in momentum:

    FΔt = Δ(mv) = m Δv
     
  6. Jan 8, 2012 #5
    Ah i tought it didn't make sense ! Ok got it ! thanks a lot :-)
     
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