2018 · Q10
Two persons are holding a rope of negligible mass horizontally. A 20 kg mass is attached to the rope at the midpoint; as a result the rope deviates from the horizontal direction. The tension required to completely straighten the rope is (g = 10 m/s2)
General KnowledgePhysics
- A200 N
- B20 N
- C10 N
- Dinfinitely large
Explanation
For the midpoint mass to be in equilibrium, the vertical components of the two rope tensions must balance its weight: 2T*sin(theta) = mg, where theta is the angle the rope makes with the horizontal. Completely straightening the rope means theta -> 0, so sin(theta) -> 0. To keep the product 2T*sin(theta) equal to the fixed weight mg, the tension T must grow without bound. Hence the required tension is infinitely large.