CBSE Class 12 Physics Solids and Fluids Assignment

CBSE Class 12 Physics Solids and Fluids Assignment. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Comprehension-1

When spherical body of mass m moving through stationary air feels forces of friction, F = kv/r, where k is constant, v is velocity of ball and r is radius of the ball. (neglect force of buoyancy)
1. If radius of ball is increasing at a rate r₀ m/sec then (Assuming initial radius to be nearly zero)

(a) ball will attain terminal velocity which is equal to √4πr₀ρ/ k where ρ is density of ball
(b) velocity will always increase
(c) behaviour of velocity can not be determined
(d) none of these

2. If radius of ball is 20 cm, k = 1 unit (M.K.S.) m = 2kg, what is maximum rate of dissipation of energy
against friction
(a) 40 J/sec (b) 80 J/sec
(c) 70 J/sec (d) can’t be determined

Comprehension-2

When a body moves in fluid with some speed it gives momentum to the fluid particles in consequence fluid applies force to the moving body which opposes the motion of the body. The opposing force can be called drag force (f_d). Drag force depends to the area of crossection (A) of the body, speed (v) of body relative to the fluid medium and density of the fluid (ρ) itself. The approximate formula can be written as f_d = CAρv² where C is a positive constant.

3. A sphere of radius r and density σ is released from rest in the fluid of density ρ, its terminal speed is

4. A small ball of radius r is floating in a tank, which is filled with liquid of density ρ and moving with constant speed v0. The tank collides with a wall and comes to rest. The velocity of the ball with which it collides with front end of tank is (neglect the jerk on the ball, when tank collides with wall)

5. Drag force on a body, which is moving in fluid is due to
(a) relative motion between the layers of fluid
(b) relative motion between the body and fluid
(c) random motion of fluid molecules
(d) Adhesive force between the body and fluid molecules

6. If the radius of the body is doubled keeping its density constant, intial dragging retardation will (assuming initial velocity to be same).
(a) increase two times (b) decrease half of its value(c) decrease by 1/ 2 ^1/3 times (d) increase by 2^1/3 times

Comprehension-3

When liquid is non viscous, non compressible and flow is steam line sum of pressure, kinetic andpotential energy per unit volume is constant i.e. P + 1/2pv² + ρgh = constant According to equation of continuity AV = constant.Water flows smoothly through the pipe shown in the figure descending in the process. Four sections of the pipe have been numbered.

7. The volume flow rate is maximum in

(a) 4 (b) 1 (c) 3 (d) same in all the four sections

8. The flow speed is maximum in
(a) 1 (b) 2 (c) 3 (d) 4

9. The water pressure is minimum in
(a) 1 (b) 2 (c) 3 (d) 4

Each of the questions given below consists of two statements, an assertion (A) and reason (R).
Select the number corresponding to the appropriate alternative as follows
(a) If both A and R are true and R is the correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) If A is true but R is false
(d) If A is false but R is true

10. A: Steel is more elastic than rubber.
R: Young’s modulus of elasticity of steel is greater than the Young’s modulus of elasticity of rubber.

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