JEE Main & Advanced
Physics
Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन
Question Bank
Surface Tension
question_answer
A thin metal disc of radius r floats on water surface and bends the surface downwards along the perimeter making an angle q with vertical edge of the disc. If the disc displaces a weight of water W and surface tension of water is T, then the weight of metal disc is [AMU (Med.) 1999]
A) \[2\pi rT+W\]
B) \[2\pi rT\cos \theta -W\]
C) \[\text{2}\pi \text{rTcos}\theta +W\]
D) \[W-2\pi rT\cos \theta \]
Correct Answer:
C
Solution :
Weight of metal disc = total upward force = upthrust force + force due to surface tension = weight of displaced water \[+Tcos\theta (2\pi r)\] \[=W+2\pi rTcos\theta \]