A stone hangs by a fine thread from the ceiling,and a section of the same thread dangles from the bottom of the stone.If a person gives a sharp pull on the dangling thread,where is the thread likely to break:below the stone or above it?

Question

Answer 1

When a sharp pull is given,alarge sudden force is applied to the bottom string and it will have a large tension acting on it. Because of the inertia of the stone, the upper string does not experience this force. Therefore,the bottom string breaks first.
If a slow and steady force is applied, the tension at the bottom string increases slowly.
The free body diagram is as shown.
At equilibrium $F_{u p} = F_{d o w n} + m g$
Thus, we see the tension on the upper string is more than the tension in the lower string because of the weight of the string acting down. Hence the string above the stone will break first.

Answer 2

Condition 1: When person gives a sharp pull -

Shape and sudden pull will cause large tension in the bottom thread and due to the inertia of the stone upper thread will not feel this force hence bottom thread will break.

Hence,

Thread will break from below the stone.

Note: Inertia of stone will play a major role here because it was in rest position and wants to be in rest position, also the mass of thread is negligible in compare with stone.

Stone is in equilibrium until the following condition -

T=F+mg

Where

T = Tension in upper thread

F = Applied force

mg = Weight of stone

Now,

When we apply slow and steady pull it increases the tension in both threads, above as well as below.

Upper thread already has tension due to weight of stone. Now applied pull will increase the total tension experienced by the upper thread than lower thread.

Hence, Thread will break from above the stone.

A stone hangs by a fine thread from the ceiling,and a section of the same thread dangles from the bottom of the stone.If a person gives a sharp pull on the dangling thread,where is the thread likely to break:below the stone or above it?

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