Answer:
1728 rev/sec
Step-by-step explanation:
The expression for the gravitational force is given by
F_g=mg_1
g_1=0.9g (Given)
therefore,

The centripetal force balances this gravitational force to keep the space station in equilibrium.
Hence we can write

Rearrange the above equation in terms of velocity

⇒

putting the values we get

v=69.65 m/sec
the rotational speed can be calculated as or frequency of rotation

putting values we get

f= 0.02 rev/sec
meaning 0.02 rev per second
therefore no. or revolution per day
= 0.02×24×3600= 1728 rev/sec