Question #350523

A 60N motor winds a cable around a drum. (I) If the cable lifts a 3-ton load of bricks to a height of 12cm in 5 sec, calculate the efficiency of the motor. (II) At what rate is work done against friction?

Expert's answer

Given:

"F=60\\:\\rm kN"

"m=3000\\:\\rm kg"

"h=0.12\\:\\rm m"

"t=5\\:\\rm s"

(a)

"\\eta=\\frac{mgh}{Fh}=\\frac{mg}{F}=\\frac{3000*9.8}{60000}=0.49=49\\%"

(b)

"P=\\frac{mgh}{t}=\\frac{3000*9.8*0.12}{5}=706\\rm\\: W"

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