Answer: 
Explanation:
The kinetic energy of an electron 
is given by the following equation:
(1)
Where:
is the momentum of the electron
is the mass of the electron
From (1) we can find :
(2)
(3)
Now, in order to find the wavelength of the electron 
with this given kinetic energy (hence momentum), we will use the De Broglie wavelength equation:
(4)
Where:
is the Planck constant
So, we will use the value of found in (3) for equation (4):
(5)
We are told the wavelength of the photon 
is the same as the wavelength of the electron:
(6)
Therefore we will use this wavelength to find the energy of the photon 
using the following equation:
(7)
Where 
is the spped of light in vacuum
Finally:
I think it is D
Hope my answer help you?
The point of contact the path difference is zero but one of the interfering ray is reflected so the effective path difference becomes λ/2 thus the condition of minimum intensity is created in the center.
Answer:
The spring force constant is 
.
Explanation:
We are told the mass of the ball is 
, the height above the spring where the ball is dropped is 
, the length the ball compresses the spring is 
and the acceleration of gravity is 
.
We will consider the initial moment to be when the ball is dropped and the final moment to be when the ball stops, compressing the spring. We supose that there is no friction so the initial mechanical energy 
is equal to the final mechanical energy 
:
Initially there is only gravitational potential energy because the force of the spring isn't present and the speed is zero. In the final moment there is only elastic potential energy because the height is zero and the ball has stopped. So we have that:
If we manipulate the equation we have that:
