Pulleys and belts. in a pulley system, pulley a is moving at 1500 rpm and has a diameter of 15 in. three pulleys, b, c, and d, all of different sizes, are attached to a single output axle. speed and torque output are changed within the system by moving the drive belt between pulleys b, c, and d.. 1.a speed of 1750 rpm is required when the drive belt is connected to pulley b. what is the diameter of pulley b? . 2.a speed of 2000 rpm is required when the drive belt is connected to pulley c. what is the diameter of pulley c? . 3.a speed of 3250 rpm is required when the drive belt is connected to?

For this question I would use the similarities between pulley A, to each pulley of the question. 

1. A speed of 1750 rpm is required when the drive belt is connected to pulley B. What is the diameter of pulley B?

15inches / 1500rpm = (x) inches / 1750rpm

(x)  = 15 inches * 1750 rpm / 1500rpm

(x) = 17.5 inches 

2.A speed of 2000 rpm is required when the drive belt is connected to pulley C. What is the diameter of pulley C?

15inches / 1500rpm = (x) inches / 2000rpm

(x)  = 15 inches * 2000 rpm / 1500rpm

(x) = 20 inches 

3. A speed of 3250 rpm is required when the drive belt is connected to?

15inches / 1500rpm = (x) inches / 3250rpm

(x)  = 15 inches * 3250 rpm / 1500rpm

(x) = 32.5 inches 

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.