The electric potential difference
required to stop an electron (called a "stopping potential") moving with an initial speed (v) of 2.85 × 10⁷ m/s is
.
How to calculate the electric potential difference?
We know, that the kinetic energy is:

where,
q is the charge

is the stopping potential
m is the mass of the electron

v is the speed of the electron
Now,

Hence, the electric potential difference is
.
To learn more about total electric potential, refer to:
brainly.com/question/16843018
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