Question Details

A uniform rope is supported by two level pin support as shown in the figure. Mass of the rope is m. Find the tension at mid-point.

Options

A

mg

B

(mg√3)/2

C

mg/4

D

mg/2

Show Answer

Correct Answer :

Option B

(mg√3)/2

(mg√3)/2

Solution :

The correct option is (mg√3)/2.

Let us analyze the forces acting on the uniform rope of mass m.

From the provided image, we can observe that the rope is supported at both ends by two level pin supports, and it makes an angle of 30° with the horizontal dotted line at both supports.

Let T0 be the tension in the rope at the supports. We can resolve this tension into vertical and horizontal components:

1. The vertical component of tension at each support is:
Ty=T0sin(30°)
2. The horizontal component of tension at each support is:
Tx=T0cos(30°)

For the vertical equilibrium of the entire rope of mass m, the total upward vertical force exerted by both supports must equal the total downward gravitational force (mg):
2T0sin(30°)=mg
Substituting the value sin(30°)=12:
2T0(12)=mg
T0=mg

Now, let us find the tension at the mid-point (the lowest point of the rope). At the mid-point, the tangent to the rope is perfectly horizontal. Therefore, the tension at this point, Tmid, is entirely horizontal.

Since there are no external horizontal forces acting on the rope, the horizontal component of the tension must be constant at every point along the rope:
Tmid=Tx=T0cos(30°)

Substituting the values of T0=mg and cos(30°)=32:
Tmid=mg(32)=mg32

Therefore, the tension at the mid-point of the rope is mg32.

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