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A mirror of weight 75N is hung by a cord from a hook on the wall. If the cord ma...


Question

A mirror of weight 75N is hung by a cord from a hook on the wall. If the cord makes an angle of 30o with horizontal, the tension in the cord is

Options

A) 100N

B) 1500N

C) 250N

D) 150N


The correct answer is D.

Explanation:

For vertical equilibrium, we have
2Ty = 75N
But Ty/T = adj/hyp = cos 60o
∴ Ty = T Cos 60o
=> 2Ty = 2Tcos 60o = 75N
2 x T x 0.5 = 75 => T = 75N
∴ Total tension in the rope = 2T.
= 2 x 75 = 150N

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Dicussion (1)

  • For vertical equilibrium, we have
    2Ty = 75N
    But Ty/T = adj/hyp = cos 60o
    ∴ Ty = T Cos 60o
    => 2Ty = 2Tcos 60o = 75N
    2 x T x 0.5 = 75 => T = 75N
    ∴ Total tension in the rope = 2T.
    = 2 x 75 = 150N

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