Help please, power (piano pulled up by workers through pulley)

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To determine the time required to lift a 3.50 kN piano 25 m using a pulley system with 75% efficiency, the effective power transmitted to the piano must be calculated. The total power exerted by three workers is 495 W, but only 75% of this is effective due to pulley friction, resulting in approximately 371.25 W available for lifting. The work done against gravity to lift the piano is 87,500 Joules (calculated as force times height). Using the effective power, the time to lift the piano can be found by dividing the work by the effective power, leading to a total lift time of approximately 235 seconds. Understanding the distinction between power and work is crucial for solving this problem accurately.
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A 3.50 kN piano is lifted by 3 workers at constant speed to an apartment 25 m above ground. Each worker is able to deliver 165 W of power and the pulley is 75% efficient (25% lost due to friction on pulley). Neglecting mass of pulley, what is the time required to lift the piano from the street to the apartment.
I know that F=T-mg=ma=0
T=3500N
Work=3*165=495W=F/t
But I'm not really sure how to sort this problem out and incorporate the 75% efficiency of the pulley and the height above ground. Please help me.
 
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xregina12 said:
Work=3*165=495W=F/t

Not quite. You are equating work (units: Joules) with power (units: Watts) here, but they are not the same. And neither of those would equal force/time.

At any rate, 495W is the power exerted by the 3 people. So how much of that power gets transmitted to the piano? (hint: it is not 100% of the power)
 

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