Need help with these problems. Thanks a lot 9. An elevator has mass 800 kg, not

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Need help with these problems. Thanks a lot

9. An elevator has mass 800 kg, not including passengers. The elevator is designed ascend, at constant speed, a vertical distance of 30.0 m in 24 seconds. It is driven by a motor that can provide up to 45 hp (I hp-746 watts) to the elevator. What is the maximum number of passengers that can ride in the elevator and have it go up at the rated speed give the motor's power rating? Assume the average passenger has a mass of 70.0 kg. (10pt) Bonus(5 pt): Consider the following figure. Block A has weight 2.0 N and Block B hasa weight of 5.0 N. The coefficient of kinetic friction between all surfaces is 0.250. What force magnitude, F, is necessary to drag Block B to the left at constant speed? Assume an ideal pulley and rope.

Explanation / Answer

Solution:

Answer (9):

Let us go to the basics first.

The force that the motor must exert on the elevator is equal to the weight of the elevator since it is moving at a constant speed. Since P = Fv, the force exerted by the motor and hence the weight of the elevator is

W = F = P/v = (45*746 watts) / (30 m /24 s) = 26856 N

The mass of the elevator is thus m = W / g = 26856 N / 9.8 = 2740.4 kg

From the problem, the number of passengers n is

n = (m - 800 kg) / 70 kg = (2740.4 kg - 800 kg) / 70 kg = 27.72

The limit is thus 27 passengers. (Answer)

Thanks!!!

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