Explanation:
Charges,

The distance between charges, r = 10 cm = 0.1 m
We need to find the magnitude and direction of the electric force. It is given by :

So, the required force between charges is 36 N and it is towards positive charge i.e. +8 μC.
Answer:
600Hz
Explanation:
In electrical systems of alternating current, the harmonics are, as in acoustics, frequencies multiples of the fundamental working frequency of the system and whose amplitude decreases as the multiple increases. For example, if we have systems fed by the 50 Hz network, harmonics of 100, 150, 200, etc. may appear.
In our case having a fundamental wave of 100Hz, I can have harmonics of 200,300,400, ..., 600Hz
Momentum is conserved if and only if sum of all forces which are exserted on system equals zero. In our situation there are only internal forces, so by Newton's third law their vector sum is 0.
So
.
Kinetic energy of system at first:
. After:
. The secret is that other energy is in work of deformation forces (they in turn heat a bullet and a block).
Answer is A)