Answer:
<em>Speed of the electron is 2.46 x 10^8 m/s</em>
<em></em>
Explanation:
momentum of the electron before relativistic effect = 
where
is the rest mass of the electron
V is the velocity of the electron.
under relativistic effect, the mass increases.
under relativistic effect, the new mass M will be
M = 
where

c is the speed of light = 3 x 10^8 m/s
V is the speed with which the electron travels.
The new momentum will therefore be
==> 
It is stated that the relativistic momentum is 1.75 times the non-relativistic momentum. Equating, we have
1.75
= 
the equation reduces to
1.75 = 
square both sides of the equation, we have
3.0625 = 1/
3.0625 - 3.0625
= 1
2.0625 = 3.0625
= 0.67
β = 0.819
substitute for 
V/c = 0.819
V = c x 0.819
V = 3 x 10^8 x 0.819 = <em>2.46 x 10^8 m/s</em>
Based on the information in the question, a light year is the distance traveled light in one year. Then if the light from the star Centauri takes 4.2 years to reach the earth, then its distance from earth is 4.2 light years.
Answer: 25N
method: total force in the right hand direction is 100N and total force in the left hand direction is 125N. To get the net force, we add forces if they are in the same direction and substract if they are in opposite directions. since 100N and 125N are in opposite directions, we substract the larger value from the smaller value. Then we get 25N in the left hand direction as the final answer.