The answer is 12.36. hoped this helped!
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
The answer is C.
The Kinetic energy which was exerted and experience pulling the string of a bow is kept as a potential energy at the end of the arrow in contact with the string. Once release from aim at stationary position the potential energy is again transformed.
Bulbs c and b would still be screwed in if they were in to begin with and bulbs A, D, and E. would be unscrewed