(a) 
The change in potential energy of the electron is given by:

where
is the magnitude of the electron's charge
is the magnitude of the electric field
d = 520 m is the distance through which the electron has moved
Substituting into the equation, we find

(b) 78 kV
The potential difference the electron has moved through is given by

where
is the magnitude of the electric field
d = 520 m is the distance through which the electron has moved
Substituting into the equation, we find

Answer:
D
Explanation:
the formula is F=mgh
so now you can write it like
m= 4×50=200
200×1.5×10=30000
Answer:

Explanation:
It is given that,
Frequency for submarine communications, f = 76 Hz
We need to find the wavelength of those extremely low-frequency waves. the relation between the wavelength and the frequency is given by :





or

So, the wavelength of those extremely low-frequency waves is 4000 km. Hence, this is the required solution.