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
.
It takes the shape of the cup and it can be sucked through a straw
The answer is 3.
When a ball is thrown into the air, there is no friction (there's nothing rubbing against it), so the only force acting on the ball is gravity, which aims to pull the ball back down. Since this is the only force, the answer will equal the gravity acting on the ball. Since "weight" is defined as just that (the gravity acting on something), the answer is 3, the magnitude of the rock's weight (or the force of gravity).
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