Explanation:
(a) The period of a wave is the time required for one complete cycle. In this case, we have the time of five cycles. So:

(b) The frequency of a wave is inversely proportional to its period:

(c) The wavelength is the distance between two successive crests, so:

(d) The speed of a wave is defined as:

Answer:B)439.21 Hz
Explanation:
Given
velocity of train 
frequency of train 
speed of sound 
frequency from Doppler effect can be calculated by





Answer:
150000000

49050000 N/C
Explanation:
q = Charge = 24 pC
m = Mass of honeybee = 0.12 g
E = Electric field = 100 N/C
g = Acceleration due to gravity = 9.81 m/s²

Number electrons is

The number of electrons added or removed was 150000000
Force is given by

The ratio is

The ratio is 
Balancing the forces we get

The electric field required is 49050000 N/C
It might be c I'm not sure either. Hope I helped