Q 11-05-165JEE MainJEE Main 2020 (7 Jan, Shift 2)Easy
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 of $3$ 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 ($g = 10\ \text{m/s}^2$) must be at least:
Answer: (D) $66000$ W
Total mass $= 10\times68 + 920 = 1600$ kg.
At constant speed the motor force balances weight and friction:
$$F = 1600\times10 + 6000 = 22000\ \text{N}$$
$$P = Fv = 22000\times3 = 66000\ \text{W}$$
Solution by Sreeraj P, M.Sc Physics