Question

A metal sphere is suspended in water at $0^{0}C$, by a thread. When water is heated to $4^{0}C$ the tension in the thread:

• A. Decreases
• B. Increases
• C. Remains same
• D. First increases and then decreases

Answer 1

The correct option is A Decreases

There are three forces acting on the sphere.
1. weight of the sphere downward
2. Tension in the thread upward
3. Buoyancy force due to the liquid upward
When water is heated from $0^0$C to $4^0$C, density of water increases. Hence, upward thrust increases since weight of the volume of water displaced increases.
Tension $+$ upward thrust $=$ weight of the metal sphere.
$\therefore$ tension in the thread decreases since sum of tension and upward thrust is constant i.e equal to the weight of the metal sphere.