Buoyancy from water. Buoyancy is an upward force on an object immersed in a fluid (i.e., a liquid or a gas), enabling it to float or at least to appear lighter.
The centripetal acceleration of an object is given by the relation,
where Ac = centripetal acceleration = 
R = radius of rotation = 15 m
V = speed of astronaut
Hence, 
solving this we get, V = 38.34 m/s
-- First, we have to decide how to handle the two resistors.
The effective resistance of resistors in series is the sum
of their individual resistances. That is, they act like a single
resistor, whose resistance is the sum of all of them.
So in this question, the 4.0 ohms and the 7.5 ohms act like a
single resistor of 11.5 ohms.
-- The current in the circuit is
(the supply voltage) / (the total resistance)
= (9.0 volts) / (11.5 ohms)
= 0.783... Ampere (rounded)
