The top makes 1200 rpm, freely falling from a height of 20 m. The number of revolutions during the fall is equal to …

Distance traveled by the top when falling:
S = V0 * t + a * t² / 2, where S is the height of the top falling (S = 20 m), V0 is the initial speed of the top (for free fall V0 = 0 m / s), t is the time the top falls, and – acceleration when the top falls (a = g = 10 m / s²).
S = V0 * t + a * t² / 2 = g * t² / 2.
t = √ (2S / g) = √ (2 * 20/10) = 2 s.
Since the top makes 1200 revolutions per minute, then in 2 seconds of falling it will make: 1200 * 2/60 = 40 revolutions.
Answer: When falling, the top will make 40 revolutions.