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?

A. 100N
B. 1500N
C. 250N
D. 150N

Correct Answer:

Option D – 150N

Explanation

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