Answer:
an experiment is a way to test a hypothesis. A hypothesis is a prediction. You predict that if you change one thing (the independent variable) the other thing (the dependent variable) will change.
The electrostatic force between two charges Q1 and q is given by

where
ke is the Coulomb's constant
Q1 is the first charge
q is the second charge
r is the distance between the two charges
Re-arranging the formula, we have

and since we know the value of the force F, of the charge Q1 and the distance r between the two charges, we can calculate the value of q:

And since the force is attractive, the two charges must have opposite sign, so the charge q must have negative sign.
The first question's answer is :
If, F=ma
Then, 15N= 2.1kg (a)
15/2.1=a
7.14=a
Therefore, acceleration = 7.14m/s^2
sorry I am not sure about the second question :-(
Heat transferred - Work done = Internal Energy
Explanation:
- If there is more heat transfer than the work done, the energy difference is called internal energy
- The first law of thermodynamics equation is given as ΔU=Q−W where, ΔU = Internal energy; Q = Heat transfer; W = Work done
- Heat = transfer of thermal energy between two bodies at different temperatures
- Work = force used to transfer energy between a system and its surroundings
- The First Law of Thermodynamics states - energy can be converted from one form to another with the interaction of heat, work and internal energy
- Energy cannot be created nor destroyed