Answer:
The magnetic field is 1.16 T.
Explanation:
speed, v = 10% of speed of light = 3 x 10^7 m/s
diameter, d = 54 cm
radius, r = 0.27 m
charge, q = 1.6 x 10^-19 C
mass, m = 1.67 x 10^-27 kg
Let the magnetic field is B.
The centripetal force is balanced by the magnetic force.

The Electromagnetic spectrum.
(a) 0.249 (24.9 %)
The maximum efficiency of a heat engine is given by

where
Tc is the low-temperature reservoir
Th is the high-temperature reservoir
For the engine in this problem,


Therefore the maximum efficiency is

(b-c) 0.221 (22.1 %)
The second steam engine operates using the exhaust of the first. So we have:
is the high-temperature reservoir
is the low-temperature reservoir
If we apply again the formula of the efficiency

The maximum efficiency of the second engine is

Water is more dense then air so it sorta holds the rock as it sinks