A horizontal force of magnitude 30.2 N pushes a block of mass 3.50 kg across a floor where the coefficient of kinetic friction is 0.646. (a)

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A horizontal force of magnitude 30.2 N pushes a block of mass 3.50 kg across a floor where the coefficient of kinetic friction is 0.646. (a) How much work is done by that applied force on the block-floor system when the block slides through a displacement of 2.96 m across the floor? (b) During that displacement, the thermal energy of the block increases by 35.2 J. What is the increase in thermal energy of the floor? (c) What is the increase in the kinetic energy of the block?

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  1. Answer:

    A) 89.39 J

    B) 30.39J

    C) 23.8 J

    Explanation:

    We are given;

    F = 30.2N

    m = 3.5 kg

    μ_k = 0.646

    d = 2.96m

    ΔEth (Block) = 35.2J

    A) Work done by the applied force on the block-floor system is given as;

    W = F•d

    Thus, W = 30.2 x 2.96 = 89.39 J

    B) Total thermal energy dissipated by the whole system which includes the floor and the block is given as;

    ΔEth = μ_k•mgd

    Thus, ΔEth = 0.646 x 3.5 x 9.8 x 2.96 = 65.59J

    Now, we are given the thermal energy of the block which is ΔEth (Block) = 35.2J.

    Thus,

    ΔEth = ΔEth (Block) + ΔEth (floor)

    Thus,

    ΔEth (floor) = ΔEth – ΔEth (Block)

    ΔEth (floor) = 65.59J – 35.2J = 30.39J

    C) The total work done is considered as the sum of the thermal energy dissipated as heat and the kinetic energy of the block. Thus;

    W = K + ΔEth

    Therefore;

    K = W – ΔEth

    K = 89.39 – 65.59 = 23.8J

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