For this item, I would assume that we asked to determine the angular deceleration of the fan. This could be answered through the equation,
d = (V² - v²) / 2a
where d is the number of revolutions made, V is the initial angular velocity, v is the final angular velocity, and a is the deceleration. Substituting,
1500 = (850² - 0²) / 2(a)
a = 240.83 rev/min
Thus, the fan's speed decreases by 240.83 rev/min.
