JEE Main · 2023 · 30 Jan 2023 · Shift 2 · Laws of Motion

A block of

3 kg

is attached to a string whose other end is attached to the wall. An unknown force F is applied so that the string makes an angle of

3 0^{\circ}

with the wall. The tension T is :
(Given

g = 10 ms^{- 2}

)

(A)20 N✓ Correct
(B)25 N
(C)10 N
(D)15 N

Answer: (A)

Solution

The junction where the strings meet is held by three forces: the tension

T

along the upper string, the horizontal applied force

F

, and the weight

3 g

of the block pulling straight down through the lower string. Because the upper string makes

3 0^{\circ}

with the vertical wall, the vertical component of the tension alone supports the weight,

T cos 3 0^{\circ} = 3 g

. With

g = 10

^{- 2}

, the tension is

T = \frac{3 \times 10}{cos 3 0 ^{\circ}} = \frac{10 3}{3 /2} = 20

JEE Main · 2023 · 30 Jan 2023 · Shift 2 · Single correct option

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