A 45 kg object is lifted vertically at a constant speed to a height of 9.0 m by a 7.5×10² w electric motor. If this motor is 25% efficient i

Question

A 45 kg object is lifted vertically at a constant speed to a height of 9.0 m by a 7.5×10² w electric motor. If this motor is 25% efficient in converting electric energy to mechanical energy, how long does the motor take to lift the object?​

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Farah 3 months 2021-09-02T04:43:37+00:00 1 Answers 0 views 0

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    2021-09-02T04:44:47+00:00

    Answer:

    the time taken for the motor to lift the object is 21.17 s.

    Explanation:

    Given;

    mass of the object, m = 45 kg

    height through which the object was lifted, h = 9.0 m

    electrical power used by the motor, P = 750 W

    Efficiency of the electrical motor, n = 25% = 0.25

    The electrical energy used by the motor in lifting the object is calculated as;

    E = P x t

    where;

    t is the time taken for the motor to lift the object

    E = 750 x t

    E = 750t

    The electrical energy converted by the motor to mechanical energy is calculated as;

    P.E = 0.25(750t)

    P.E = 187.5t

    Recall, P.E = mgh

    mgh = 187.5t

    45 x 9.8 x 9 = 187.5t

    3969 = 187.5t

    t = 3969/187.5

    t = 21.17 s

    Therefore, the time taken for the motor to lift the object is 21.17 s.

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