Answer:
C) Use two batteries instead of one.
Explanation:
-Strength of an electromagnet depends on the electrical current which flows through the wires.
-Two batteries have a higher current than one and thus higher strength in the electromagnet.
Answer:
A stone that is dropped down into an empty well
To calculate the force between two negative charges, we use the formula which is given by the Coulomb`s Law as
Here, 
and
are the charges on the pith balls, r is the separation between the charges and k is constant and its value is 
.
Given 
and 
.
Substituting these values in above formula we get,
Thus, the repulsive force between two pith balls is 
.
It is either the mass or density, I believe it is 3 density tho but it could be mass good luck:)
