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Properties of Matter question

2021 · 27 Jul · Shift 1 · Q59
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  5. /2021 · 27 Jul · Shift 1 · Q59

Properties of Matter question

2021 · 27 Jul · Shift 1 · Q59

JEE MainPhysicsProperties of MatterMCQ+4 / −1
A light cylindrical vessel is kept on a horizontal surface. Area of base is A. A hole of cross-sectional area 'a' is made just at its bottom side. The minimum coefficient of friction necessary to prevent sliding the vessel due to the impact force of the emerging liquid is (a < < A) : JEE Main 2021 (Online) 27th July Morning Shift Physics - Properties of Matter Question 180 English
  1. A
    A2a{A \over {2a}}2aA​
  2. B
    None of these
  3. C
    2aA{{2a} \over A}A2a​
  4. D
    aA{{a} \over A}Aa​
View written solutionFree

Correct answer: C

  1. Speed of efflux from the hole

If the liquid level above the hole is hhh, then by Torricelli’s theorem the speed of the emerging liquid is

v=2gh.v = \sqrt{2gh}.v=2gh​.

  1. Mass of liquid emerging per second

The hole has area aaa, so volume flow rate is

Q=av.Q = av.Q=av.

Hence mass flow rate is

m˙=ρav,\dot m = \rho av,m˙=ρav,

where ρ\rhoρ is the density of the liquid.

  1. Horizontal reaction on the vessel due to jet

The jet carries horizontal momentum. So the reaction force on the vessel is

F=m˙ v=(ρav)(v)=ρav2.F = \dot m \, v = (\rho av)(v) = \rho a v^2.F=m˙v=(ρav)(v)=ρav2.

Using v2=2ghv^2 = 2ghv2=2gh,

F=ρa(2gh)=2ρagh.F = \rho a(2gh) = 2\rho agh.F=ρa(2gh)=2ρagh.

  1. Normal reaction on the vessel

The vessel is light, so only the liquid contributes significantly to the weight.

Weight of liquid in the vessel:

W=ρ(Ah)g=ρAgh.W = \rho (Ah) g = \rho Agh.W=ρ(Ah)g=ρAgh.

So normal reaction from the ground is

N=ρAgh.N = \rho Agh.N=ρAgh.

  1. Condition for no sliding

Maximum static friction is

fmax⁡=μN=μρAgh.f_{\max} = \mu N = \mu \rho Agh.fmax​=μN=μρAgh.

To prevent sliding,

fmax⁡≥F.f_{\max} \ge F.fmax​≥F.

So,

μρAgh≥2ρagh.\mu \rho Agh \ge 2\rho agh.μρAgh≥2ρagh.

Cancel ρgh\rho ghρgh:

μA≥2a\mu A \ge 2aμA≥2a

μmin⁡=2aA.\mu_{\min} = \frac{2a}{A}.μmin​=A2a​.

  1. Match with options

μmin⁡=2aA\boxed{\mu_{\min} = \frac{2a}{A}}μmin​=A2a​​

So the correct option is C.

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