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A light (massless) cylindrical vessel rests on a horizontal floor. Its base has area A. A hole of cross-sectional area 'a' is opened right at the bottom on the side. Owing to the reaction (thrust) of the emerging water jet the vessel tends to slide. Taking a << A, the minimum coefficient of friction between vessel and floor needed to keep it from sliding is:
- A/(2a)
- None of these
- 2a/A
- a/A
Correct answer: 2a/A
Solution
The escaping jet exerts a reaction force on the vessel; for it not to slide, static friction (mu times the weight of water resting on the base) must at least equal that thrust.
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