Answer:
4.80 seconds
Explanation:
The velocity of sound is obtained from;
V= 2d/t
Where;
V= velocity of sound = 329.2 ms-1
d= distance from the wall = 790.5 m
t= time = the unknown
t= 2d/V
t= 2 × 790.5/ 329.2
t= 4.80 seconds
The De Broglie wavelength of the electron is

And we can use De Broglie's relationship to find its momentum:

Given

, with m being the electron mass and v its velocity, we can find the electron's velocity:

This velocity is quite small compared to the speed of light, so the electron is non-relativistic and we can find its kinetic energy by using the non-relativistic formula:
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