b) i) What is the S.I unit of moment of force?
S.I. unit of the moment of force is Newton x meter (Nm)
A small stone of mass m = 200 g is held under water in a tall jar and is allowed to fall as shown in the figure. The free body diagram of the stone is also shown:
i) What do F2 and m1 represent?
ii) Calculate the net force acting on the stone and
iii) its acceleration as it falls through water. (Neglect the force due to viscosity. Take the volume of the stone as 80 cm3, density of water as 1.0 g/cm3 and acceleration due to gravity, g = 10 m/s2.
i)
Here in this case,
F2 represents the upthrust and m2 represents the mass.
ii)
Therefore,
Net force = 2 N – 0.8 N = 1.2 N
iii) Acceleration, a = 
Name the factors affecting the turning effect of a body?
The factors affecting the turning effect of a body are:
i) The magnitude of a force applied.
ii) The distance of the line of action of the force from the axis of rotation.
When a body is placed on a table top, it exerts a force equal to its weight downward on the table top but does not move or fall.
i) Name the force exerted on the table top.
ii) What is the direction of the force?
i) Normal reaction force
ii) The force acts normal to the surface of the table top i.e., opposite to the direction of the force due to the weight of the body.
State Newton’s second law of motion both in words and in equation form. Under what condition does this equation become F = ma?
Newton’s second law of motion states that the rate of change of momentum of a body is directly proportional to the force applied on the body and it takes place in the direction of the force. 
Thus, it becomes equal to ma when mass is constant.
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