Answer:
The electric force between them if the pieces of grain are 2 cm apart is 
.
Explanation:
Given:
Charge on one grain, 
Charge on another grain, 
Separation between them, 
Electric force acting between two charges 
separated by a distance 
is given as:
Where, 
is Coulomb's constant equal to 
.
Now, plug in all the values and solve for 
.
Therefore, the electric force between them if the pieces of grain are 2 cm apart is .
Place the permanent magnet into an AC magnetic field and slowly reduce the field to 0 and the magnet will be temporarily demagnetized.
Momentum = mass x velocity
Before collision
Momentum 1 = 2 kg x 20 m /s = 40 kg x m/s
Momentum 2 = 3 kg x -10m/s = -30 kg x m/s
After collision
Momentum 1 = 2 kg x -5 m/s = -10 m/s
Momentum 2 = 3 kg x V2 = 3V2
Total momentum before = total momentum after
40 + -30 = -10 + 3V2
V2 = <span>6.67 m/s
Total kinetic energy before
</span><span>= (1/2) [ 2 kg * 20 m/s * 2 + 3 kg * ( -10 m/s) *2 ]
= 550 J
</span>
<span>Total kinetic energy after
</span>= (1/2) [ 2 kg * ( - 5 m/s) * 2 + 3 kg * 6.67 m/s *2 ]
= 91.73 J
Total kinetic energy lost during collision
=<span>550 J - 91.73 J
= 458.27 J</span>
The graph shows the production of Fe.
You can see from the graph that it increases rapidly and then slowly increases.
The answer is (A).
Cheers.
