Question

An elevator in a building can carry a maximum of 10 persons, with the average mass of each person being 68 kg. The mass of the elevator itself is 920 kg and it moves with a constant speed 3 m/s. The frictional force opposing the motion is 6000 N. If the elevator is moving up with its full capacity, the power delivered by the motor to the elevator (g = 10 m/s²) must be at least : 

(1) 56300 W

(2) 48000 W

(3) 66000 W

(4) 62360 W

Answer 1

Answer is (3) 66000 W

elevater moving with constant speed hence

T = 6800 + 9200 + 6000

T = 22000 N

power = T·v = 22000 × 3

= 66000 W

Answer 2

Answer is (3) 66000 W

Net force on motor will be

F_m = [920 + 68(10)]g + 6000

= 22000 N

So, required power for motor

P_m = vector(F_m.v)

= 22000 × 3

= 66000 watt