An electric motor lifts a 1 000 kg elevator at a speed of 3.0 m/s. If the motor

Question

An electric motor lifts a 1 000 kg elevator at a speed of 3.0 m/s. If the motor uses 50 kW of power to do this, its efficiency is about: A) 16: B) 20% D) none of these 17. Three resistors, each with R 300 2, are connected in parallel to a 120 V potential. The C), 1 200 mA D) none of these 6.0% C)40% ing fi lum's total current flowing through the circuit will be: A) 130 mA An object of mass m is at an altitude equal to the radius of the Earth above the Earth's B) 400 mA 18. surface. If it is released from rest it will hit the Earth's surface at a speed of: D) none of these t at osi the Assuming that the moon is mass m and orbits the Earth (mass M) in a circular path of radius r, then the orbital angular momentum of the moon with respect to the Earth is 19. je D) none of these 20. An object of mass 2.0 kg increases its speed from 10 m/s to 20 m/'s in a time of 5.0 s. The total work done on the object during this time interval is: A) 100 J B) 60 J C) 300 J D) none of these

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16.

Output power

P=FV =mgV(1000*10)*3 =30000 Watss

Efficency

n=(Pout/Pin)*100 =(30000/50000)*100

n=60 %

17.

equivalent resistance

1/R =1/300 +1/300 +1/300

R=100 ohms

Total current

I=V/R =120/100 =1.2 A

I=1200 mA (since 1 A=1000 mA)

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