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
Answer:
the force of gravity between them is quadrupled .
Explanation:
Since gravitational force is inversely proportional to the square of the separation distance between the two interacting objects, more separation distance will result in weaker gravitational forces.
Answer:
Tangential speed=5.4 m/s
Radial acceleration=
Explanation:
We are given that
Angular speed=2.59 rev/s
We know that
1 revolution=
2.59 rev=
By using 
Angular velocity=
Distance from axis=r=0.329 m
Tangential speed=
Radial acceleration=
Radial acceleration=