These are known as balanced forces because they will not change the motion of the object, and it will remain at rest unless forces become unbalanced- meaning they would be unequal and not opposing.
Answer:
A) B = 5.4 10⁻⁵ T, B) the positive side of the bar is to the West
Explanation:
A) For this exercise we must use the expression of Faraday's law for a moving body
fem = 
fem =
- d (B l y) / dt = - B lv
B = 
we calculate
B = - 7.9 10⁻⁴ /(0.73 20)
B = 5.4 10⁻⁵ T
B) to determine which side of the bar is positive, we must use the right hand rule
the thumb points in the direction of the rod movement to the south, the magnetic field points in the horizontal direction and the rod is in the east-west direction.
Therefore the force points in the direction perpendicular to the velocity and the magnetic field is in the east direction; therefore the positive side of the bar is to the West
First we gotta use an equation of motion:

Our vertical distance d= 100 m, initial vertical speed u = 0 m/s (because velocity is fully horizontal), and vertical acceleration a = 9.8 m/s2 because of gravity. Let's plug it all in!

Now we just need to solve for t:

Hit the calculators, and you'll get 4.5 seconds!
Answer: The speed necessary for the electron to have this energy is 466462 m/s
Explanation:
Kinetic energy is the energy posessed by an object by virtue of its motion.

K.E= kinetic energy = 
m= mass of an electron = 
v= velocity of object = ?
Putting in the values in the equation:


The speed necessary for the electron to have this energy is 466462 m/s