Principle of conservation of linear momentum can be deduced from Newton's

To study the third law of motion, the following sets of apparatus are available in a laboratory.

Set (i) One spring balance, two weight boxes, inextensible thread, one pulley with a clamp, two pans of known mass.

Set (ii) Two identical spring balances, one weight box, inextensible thread, one frictionless pulley with a clamp, one pan of known mass, rigid support.

Set (iii) Four identical spring balances, two pulleys, inextensible thread, two clamps, two pans of known masses, two rigid support.

Set (iv) Two identical spring balances, two weight boxes, two rigid supports, two pans of known masses, inextensible thread, two frictionless pulleys with clamps.

To perform the experiment successfully by using minimum apparatus, the best choice would be: 

For doing the experiment "to study the third law of motion using two spring balances", four students A, B, C and D set up their apparatus as shown below. The best setup is that of student.

(A) 

(B) 

(C) 

(D) 

Which of the forces involved in dragging a heavy object on a smooth, horizontal surface, have the same magnitude?

Body A collides with a body B. A exerts a force of $10 \mathrm{N}$ on B. The force which B exerts on A is _____ $\mathrm{N}$.