# Reynold's Number

## Trending Questions

**Q.**What is a pseudo force?

**Q.**

An airplane, taking off from a field, has a run of 500 m. What is the acceleration if he leaves the ground in 10 s from the start? Also find the take-off velocity.

**Q.**What is the net force on the coil

- 25×10−7N moving towards wire

- 25×10−7N moving away from wire

- 35×10−7N moving towards wire

- 35×10−7N moving away from wire

**Q.**The ratio of inertial forces to viscous forces is known as

- Coefficient of viscosity
- Reynolds number
- Fluid compressibility
- None of these

**Q.**A heavy brass sphere is hung from a spring and it executes vertical vibrations with period T. The sphere is now immersed in a non-viscous liquid with a density 110th that of brass. When set into vertical vibrations with the sphere remaining inside liquid all the time, the time period will be:

- √910T
- √109T
- 910T
- Unchanged

**Q.**

A bullet of mass $20g$ has an initial speed of $1m/s$, just before it starts penetrating a mud wall of thickness $20cm$. if the wall offers a mean resistance of $2.5\times {10}^{-2}N$, the speed of the bullet after emerging from the other side of the wall is close to:

$0.4m/s$

$0.1m/s$

$0.3m/s$

$0.7m/s$

**Q.**

The distance $x$ covered by a particle in one dimension motion varies as with time as ${x}^{2}=a{t}^{2}+2bt+c$, where $a,b,c$ are constants. Acceleration of particle depend on $x$ as ${x}^{-n}$, the value of $n$ is;

**Q.**Consider two solid spheres P and Q each of density 8gmcm−3 and diameters 1cm and 0.5cm respectively. Sphere P is dropped into a liquid of density 0.8gmcm−3 and viscosity η=3 poiseulles. Sphere Q is dropped into a liquid of density 1.6gmcm−3 and viscosity η=2 poiseuille. The ratio of the terminal velocities of P and Q is

**Q.**Calculate Reynolds number, if a fluid having viscosity of 0.5 Ns/m2 and density of 450 kg/m3, flows through a pipe of 20 mm diameter with an average velocity of 2.5 m/s.

- 225
- 90
- 45
- 144

**Q.**

A solid sphere of radius 5 cm floats in water. If a maximum load of 0.1 kg can be put on it without wetting the load, find the specific gravity of the material of the sphere.

**Q.**One end of a massless rope, which passes over a massless and frictionless pulley P is tied to a hook C while the other end is free. Maximum tension that the rope can bear is 360 N. with what value of minimum safe acceleration (in ms−2 can a monkey of move down on the rope

- 16
- 6
- 4
- 8

**Q.**

Two small balls A and B, each of mass m, are joined rigidly to the ends of a light rod of length L (figure 10-E10). The system translates on a frictionless horizontal surface with a velocity v0 in a direction perpendicular to the rod. A particle P of mass m kept at rest on the surface sticks to the ball A as the ball collides with it. Find (a) the linear speeds of the balls A and B after the collision, (b) the velocity of the centre of mass C of the system A + B + P and (c) the angular speed of the system about C after the collision.

**Q.**

3. When a projectile is at the highest point on its trajectory, the potential and kinetic energies are respectively a) maximum and minimum b) minimum and zero c) zero and maximum d) maximum and zero

4. A block of mass 2 kg starts moving when the angle of inclination of the inclined plane is 60o . If the coefficient of kinetic friction is 0.6, the frictional force is a) 2 N b) 1 N c) 4 N d) 0.5 N 5. Two forces F1 = (7i + 2j) N and F2 = (-5i + 3j) N act on a particle. The third force F3 that should act on the particle to make it move with constant velocity is a) (2i + 5j) N b) (-2i – 5j) N c) (–2i + 5j) N d) (2i – 5j) N 6. Two satellites of masses 3M and M orbit the earth in circular orbits of radii r and 3r respectively. The ratio of their speeds is a) 1 : 1 b) : 1 c) 3 : 1 d) 9 : 1 7. In an adiabatic process, the pressure of a gas is proportional to the cube of its absolute temperature. The value of (which equals Cp/Cv) is a) 5/4 b) 4/3 c) 5/3 d) 3/2 Space for rough work AEE15vA 4 8. A mass is moving towards the origin along the x-axis with constant velocity. Its angular momentum with respect to the origin a) remains constant b) is zero c) increases d) decreases 9. The rate of cooling of a liquid is 4o C/s, when its temperature is 80o C and is 2o C/s when its temperature is 50o C. The temperature of the surrounding is a) 30o C b) 20o C c) 10o C d) 25o C 10.A Charged sphere of radius 1m carries a charge of 1 x 10-9 C. The electric fields at a point P, which is at a distance d = 3m from the centre of the sphere and at a point Q, at a distance d = 0.3m from the centre of the sphere are respectively a) 1 N/C and 100 N/C b) 1 N/C and zero c) zero and 1 N/C d) 1 N/C and 3 N/C 11.An electric dipole lying along X-axis with moment 5 Am2 is subjected to an electric field of magnitude 10j N/C. The torque experienced is a) 2 Nm b) 10 Nm c) 50 Nm d) 25 Nm 12.A parallel plate capacitor with air gap of 5 mm is 2 MFD. If a metallic plate of thickness 3 mm is inserted in between the plates, the new capacitance is a) 5 MFD b) 1 MFD c) 2 MFD d) 2.5 MFD 14. Two resistances 6Ω and 3Ω are connected in parallel and this combination is connected in series with a 4Ω resistance. This combination is powered by a voltage source of 12 V and zero internal resistance. The ratio of power dissipated between 6Ω resistance and 4Ω resistance is a) 1:4 b) 4:1 c) 1:8 d) 3:215. Two charged particles of charge ratio 1:4 moving with same velocity enter a region of uniform magnetic field of strength B and get deflected and move along curves with equal radius R. The ratio of their masses is a) 4:1 b) 2:1 c) 1:4 d) 1:2 16. When a charged particle moves in a region with electric field E = 3i N/C and magnetic field B = 5j T, the trajectory of the particle is a) circle b) parabola c) straight line d) helix 17. Two co-axial coils A and B of radius R1 and R2 carry equal amount of current but flowing in opposite direction. The net magnetic field produced at the centre of these coils is zero. The ratio of the current flowing in the coil A to current in coil B is a) R1 : R2 b) R2 : R1 c) (R2 / R1) 2 d) (R1 / R2) 2 20.An object of size 10 cm is kept at a distance of 10 cm from a convex lens. If the focal length of the lens is 5 cm, the size of the image is a) 10 cm b) 20 cm c) 5 cm d) 15 cm 21.A biconvex lens of focal length 10 cm is to be made from a glass material. If the refractive index of the material is 1.5, what must be the radius of curvature of the surface of the lens? a) 0.1 m b) 0.15 m c) 0.20 m d) 0.30m22.A diffraction grating with 106 lines / m is used to determine the wavelength of a monochromatic source. The angle of first order diffraction is 30o . The wavelength of the source is a) 1000 nm b) 500 nm c) 400 nm d) 600 nm 23.A glass plate of thickness 1.5 μm and refractive index 1.5 is introduced between one of the slits and screen in a Young’s double slit experiment. If the wavelength of the monochromatic source used is = 0.75 μm, the phase difference between the interfering waves at the centre of the screen is equal to a) 6 b) 3 c) d) 2 24. What is the velocity of light in a medium with refractive index 1.5? a) 2 x 108 m/s b) 3 x 108 m/s c) 1.5 x 108 m/s d) 2.5 x 108 m/s 25. Which among the following electromagnetic radiations is the most energetic? a) Infra red light b) Visible light c) Ultraviolet light d) microwaves 26. Which of the following particles has the shortest de-Broglie wavelength, if all of them move with same speed? a) beta particle b) alpha particle c) proton d) neutron 27. The mass of a photon of wavelength is given by a) h /c b) /hc c) h/ c d) hc/ 28. The radius of a nucleus with A = 256 is 8 fermi (1 fermi = 1 x 10-15 m). The radius of a nucleus with A = 4 is a) 1 fermi b) 2 fermi c) 3 fermi d) 4 fermi 29. Photons of energy 6 eV fall on the surface of a metal with work function 4 eV. The stopping potential of the metal surface is a) 2 V b) 10 V c) 3 V d) 1 V

**Q.**

Explain Archimedes principle?

**Q.**The Reynolds number for laminar flow is

- More than 2100
- Less than 2100
- More than 4000
- Between 2100 and 4000

**Q.**Calculate Reynold’s number, if a fluid having a viscosity of 0.4 Ns/m2 and density of 900 kg/m3 flows through a pipe of length 20 mm with a velocity of 2.5 m/s.

- 130
- 121.5
- 112.5
- 100

**Q.**

A rocket has a mass of 100 kg. 90% of this is fuel. It ejects fuel vapours at therate of 1 kg/sec with a velocity of 500 m/sec relative to the rocket. It is supposed that the rocket is outside the gravitational field. The initial upthrust on the rocket when it just starts moving upwards is

Zero

500 N

1000 N

2000 N

**Q.**

A smooth wedge A is fitted in a chamber hanging from a fixed ceiling near the earth's surface.. A block B placed at the top of the wedge takes time T to slide down the length of the wedge. If the block is placed at the top of the wedge and the cable supporting the chamber is broken at the same instant, the the block will

(a) take a time longer than T to slide down the wedge

(b) take a time shorter than time T to slide down the wedge

(c) remain at the top of the wedge

(d) Jump off the wedge.

The answer is (a).

**Q.**

An object moves in a straight line according to the equation, x = 2 t3 - 3 t2 - 6t, where x is in meter and t is in second. At what time is the acceleration of the object zero?

t = 0.5 s

t = 1.0 s

t = 2.0 s

2.5 s

**Q.**Water flows through two identical tubes A and B. Water of volume V0 passes through the tube A and volume 2V0 through tube B in a given time interval. Which of the following options given is/ are possible?

- Flow in both the tubes is steady.
- Flow in both the tubes is turbulent.
- Flow is steady in A but turbulent in B.
- Flow is steady in B but turbulent in A.

**Q.**

What is the subject that deals with mass, velocity, and energy?

**Q.**A man drops an apple in the lift. He finds that the apple remains stationary and does not fall. The lift is

- Going down with constant speed.
- Going up with constant speed
- Accelerating down with acceleration g.
- Accelerating up with acceleration g.

**Q.**An oil drop falls through air with a terminal velocity of 5×10−4 m/s. Viscosity of oil is 1.8×10−5 Ns/m2 and density of oil is 900 kg/m3. Neglecting density of air as compared to that of the oil, choose the correct statements.

- Radius of the drop is 6.20×10−2 m
- Radius of the drop is 2.14×10−6m
- Terminal velocity of the drop at half of this radius is 1.25×10−4 m/s
- Terminal velocity of the drop at half of this radius is 2.5×10−4 m/s

**Q.**A small sphere of radius r falls from rest in a viscous liquid. Heat is produced due to friction between the liquid and the sphere. Choose the correct relation between rate of production of heat and the radius of the sphere, when terminal velocity is attained.

- dQdt∝r2
- dQdt∝r5
- dQdt∝r3
- dQdt∝(r)32

**Q.**

Two spheres of mass $10g$ and $100g$ each falls on the two pans of a table balance from a height of $40cm$ and $10cm$, respectively. If both are brought to rest in $0.1second$, determine the force exerted by each sphere on the pans.

**Q.**

If a ball is thrown upwards from the surface of the earth then initially

a)The earth remains stationary while the ball moves upwards

b)The ball remains stationary while the earth moves downwards

c)The ball and earth both move toward each other

d)The ball and earth both move away from each other

Also explain why and how

**Q.**

(a) What is the largest average velocity of blood flow in an artery of radius 2×10–3 m if the flow must remain laminar? (b) What is the corresponding flow rate? (Take viscosity of blood to be 2.084×10–3 Pa s).

**Q.**

A piston of a syringe pushes a liquid with a speed of 1 cm/sec. The radii of the syringe tube and the needle are R = 1cm and r = 0.5 mm respectively. The velocity of the liquid coming out of the needle is

2 cm/sec

400 cm/sec

None of these

10 cm/sec

**Q.**The Reynolds number of a flow is the ratio of

- Gravity to viscous force
- Gravity force to pressure force
- Inertia force to viscous force
- Viscous forces to pressure forces

**Q.**If a fluid having viscosity 0.6 Ns/m2 and density of 900 kg/m3, flows through a pipe of diameter 40 mm, then find the maximum velocity of fluid (in m/s) inside the pipe for laminar flow. (Critical Reynold's number =2100)

- 35
- 90
- 46.6
- 31.5