Question

To study the third law of motion, 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, a 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 :

• A. Set(i)
• B. Set(ii)
• C. Set(iii)
• D. Set(iv)

Answer 1

The correct option is B

Set(ii)

1. Newton's third law states that for every action, there is an equal and opposite reaction.
2. To measure action and reaction force only two spring balances are required.
3. To apply force on the spring balance only one pan of known mass is required.
4. Inextensible thread is also required along with one frictionless pulley with a clamp to suspend the mass at one end of the spring balance.
5. A rigid support is also required to fix the spring balance.
6. So, the set best matches are set(ii)
7. 

Thus, option (b) is correct.