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31 December, 22:15

A bucket that has a mass of 30 kg when filled with sand needs to be lifted to the top of a 30 meter tall building. You have a rope that has a mass of 0.3 kg/m that must be secured to the bucket. It takes 1 meter of rope to secure the bucket. Once the bucket reaches the top of the building it only has mass 15 kg because there was a hole in the bottom and sand was leaking out at a constant rate while it was being lifted to the top of the building. Find the work done lifting the bucket (sand and rope) to the top of the building.

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  1. 31 December, 22:17
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    765 J

    Step-by-step explanation:

    We are given;

    Mass of bucket = 30 kg

    Mass of rope = 0.3 kg/m

    height of building = 30 meter

    Now,

    work done lifting the bucket (sand and rope) to the building = work done in lifting the rope + work done in lifting the sand

    Or W = W1 + W2

    Work done in lifting the rope is given as,

    W1 = Force x displacement

    W1 = (30,0) ∫ (0.2x. dx)

    Integrating, we have;

    W1 = [0.2x²/2] at boundary of 30 and 0

    W1 = 0.1 (30²)

    W1 = 90 J

    work done in lifting the sand is given as;

    W2 = (30,0) ∫ (F. dx)

    F = mx + c

    Where, c = 30 - 15 = 15

    m = (30 - 15) / (30 - 0)

    m = 15/30 = 0.5

    So,

    F = 0.5x + 15

    Thus,

    W2 = (30,0) ∫ (0.5x + 15. dx)

    Integrating, we have;

    W2 = (0.5x²/2) + 15x at boundary of 30 and 0

    So,

    W2 = (0.5 * 30²) / 2) + 15 (30)

    W2 = 225 + 450

    W2 = 675 J

    Therefore,

    work done lifting the bucket (sand and rope) to the top of the building,

    W = 90 + 675

    W = 765 J
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