EASY
Earn 100

A parachute descend slowly because it has a large surface area coming down fast so the air which collides with that surface exerts force on that surface in _____ direction so its speed of coming down also gets reduced.

50% studentsanswered this correctly

Important Questions on Mechanical Properties of Fluids

MEDIUM
A solid sphere, of radius R acquires a terminal velocity v1 when falling (due to gravity) through a viscous fluid having a coefficient of viscosity η. The sphere is broken into 27 identical solid spheres. If each of these spheres acquires a terminal velocity, v2, when falling through the same fluid, the ratio v1v2 equals:
MEDIUM
Two solid spheres of the same metal but of mass M and 8M fall simultaneously in a viscous liquid. The ratio of terminal velocity of the second sphere to that of the first sphere is
MEDIUM
Which of the following option correctly describes the variation of the speed υ and acceleration 'a' of a point mass falling vertically in a viscous medium that applies a force F=-kυ , where 'k' is a constant, on the body? (Graphs are schematic and not drown to scale)
MEDIUM
A rain drop of radius 0.3 mm has a terminal velocity in air of 1 m s-1. The viscosity of air is 8×10-5 poise. The viscous force on it is
HARD
Two tubes of radii r1 and r2 and lengths l1 and l2, respectively, are connected in series and a liquid flows through each of them in stream line conditions. P1 and P2 are pressure differences across the two tubes. If P2 is 4P1 and l2 is l 1 4 then the radius r2 will be equal to :
MEDIUM
If a ball of steel density (ρ=7.8 g cm-3) attains a terminal velocity of 10cms-1 when falling in a tank of water (coefficient of viscosity ɳwater=8.5×10-4 Pa-s) then its terminal velocity in glycerine

(ρ=12 g cm-3, ɳ=13.2 Pa-s) would be nearly
MEDIUM
A small sphere of mass m is dropped from a great height. After it has fallen 100 m, it has attained its terminal velocity and continues to fall at that speed. The work done by air friction against the sphere during the first 100 m of fall is
MEDIUM
The terminal speed of a sphere of gold (density=19.5 kg  m-3) is 0.2 ms-1 in a viscous liquid (density=1.5 kg m-3). Then the terminal speed of a sphere of silver (density=10.5 kg m-3) of the same size in the same liquid is
MEDIUM
Eight equal drops of water are falling through air with a steady velocity of 10 cms-1. if the drops combine to form a single drop big size, then the terminal velocity of this big drop is
HARD

A solid sphere moves at a terminal velocity of 20 m s-1 in air at a place where g=9.8 m s-2The sphere is taken in a gravity free hall having air at the same pressure and pushed down at a speed of  20 m s-1.

MEDIUM
In Millikan's oil drop experiment, an oil drop of mass 16×10-6 kg is balanced by an electric field of 106 V m-1. The charge in coulomb on the drop is (assuming g=10 m s-2)
MEDIUM
A spherical ball of radius 1×10-4 m and density 104 kg m-3 falls freely under gravity through a distance h before entering a tank of water. If after entering the water the velocity of the ball does not change, find h. The viscosity of water is 9.8×10-6 Nsm-2.
MEDIUM
Spherical ball of radius R are falling in a viscous fluid of viscosity ɳ with a velocity v. The retarding viscous force acting on the spherical ball is
MEDIUM
A tiny spherical oil drop carrying a net charge q is balanced in still air with a vertical uniform electric field of strength 81π7×105 V m-1. When the field is switched off, the drop is observed to fall with terminal velocity 2×10-3  m s-1. Given  g=9.8 m s-2, viscosity of the air 1.8×10-5 N s m-2 and the density of oil  =900 kg m-3, the magnitude of q is
MEDIUM
An iron sphere of mass 20×10-3kg falls through a viscous liquid with terminal velocity 0.5 ms-1. The terminal velocity ( in ms-1) of another iron sphere of mass 54×10-2 kg is
HARD

Two solid spheres A and B of equal volumes but of different densities dA and dB are connected by a string. They are fully immersed in a fluid of density dF. They get arranged into an equilibrium state as shown in the figure with a tension in the string. The arrangement is possible only if:

Question Image

 

MEDIUM
What will be the approximate terminal velocity of a rain drop of diameter 1.8×10-3m , when density of rain water 103kgm-3 and the coefficient of viscosity of air 1.8×10-5N-sm-2 ? Neglect buoyancy of air
EASY
In Millikan's oil drop experiment a drop of charge Q and radius r is kept constant between two plates of potential difference of 800 V. Then charge on other drop of radius 2r which is kept constant with a potential difference of 3200 V is
MEDIUM
Eight drops of a density ρ and each of radius a are falling through air with a constant velocity 375cm s-1. When the eight drops coalesce to from a single drop the terminal velocity of the new drop will be
MEDIUM
A sphere of mass M and radius R is dropped in a liquid, then terminal velocity of sphere is proportional to