In the second 30 mins, the speed should be 20 + 1.5 = 21.5 km/h
So S = 21.5 * 30/60 = 10.75 km
Explanation:
It is given that,
Kinetic energy of the electron, 
Let the east direction is +x direction, north direction is +y direction and vertical direction is +z direction.
The magnetic field in north direction, 
The magnetic field in west direction, 
The magnetic field in vertical direction, 
Magnetic field, 
Firstly calculating the velocity of the electron using the kinetic energy formulas as :



(as it is moving from west to east)
The force acting on the charged particle in the magnetic field is given by :


Since, 
And, 
![F=1.6\times 10^{-19}\times [1178 k-2864.20j]](https://tex.z-dn.net/?f=F%3D1.6%5Ctimes%2010%5E%7B-19%7D%5Ctimes%20%5B1178%20k-2864.20j%5D)


(b) Let a is the acceleration of the electron. It can be calculated as :



Hence, this is the required solution.
-di represents an image in front of a lens
You must observe the object twice.
-- Look at it the first time, and make a mark where it is.
-- After some time has passed, look at the object again, and
make another mark at the place where it is.
-- At your convenience, take out your ruler, and measure the
distance between the two marks.
What you'll have is the object's "displacement" during that period
of time ... the distance between the start-point and end-point.
Technically, you won't know the actual distance it has traveled
during that time, because you don't know the route it took.