The old electricity meters with disk using sapphire bearings for friction to be minimal to not aggravate metering
Answer:
a solution
Explanation: A solution is a homogeneous mixture consisting of a solute dissolved into a solvent .
Answer:
fo = 378.52Hz
Explanation:
Using Doppler effect formula:

where
f' = 392 Hz
C = 340m/s
Vb = 20m/s
Va = 31m/s
Replacing these values and solving for fo:
fo = 378.52Hz