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    ShaRain's Avatar
    ShaRain Posts: 1, Reputation: 1
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    #1

    Nov 14, 2012, 09:14 PM
    Physics problems solver
    A horizontal force of 20 N drags a small sled 42 m across the ice at constant speed. Find the work done by the pulling force and the friction force. What is the resultant force?
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    harum Posts: 339, Reputation: 27
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    #2

    Nov 24, 2012, 07:07 PM
    If the speed of a small sled is always constant, then this means that acceleration a = 0 m/s^2.

    From F = m*a it follows that the resulting force F is m*0, which is also 0. Hence, pulling force is equal to the friction force in the magnitude. However, they are opposite in the direction.

    m*0 = F(res.) = F(pull) + F(friction) = 0

    F(pull) = - F(friction) = 20N. Forces are equal in magnitude and therefore, the work they have done is also equal in absolute value.

    Work by a force W = F*s.

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