CBSE Class 11 Physics Worksheet Set 03 Solved

1. What does the shape of stress Vs strain graph give? 

2. Railway tracks are laid on large sized wooden sleepers. Why? 

3. Why two streamlines cannot cross each other? 

4. Why two boats moving in parallel directions close to each other get attracted? 

5. Define coefficient of viscosity of a liquid. 

6. A steel wire of 4.0m is stretched through 2.0mm. The cross-sectional area of the wire is 2.0mm². If Y of steel is 2.0x10¹¹Nm^-2, find (i) the energy density of the wire & (ii) the elastic potential energy stored in the wire.

7. Represent graphically the variation of extension with load in an elastic body. On the graph mark: (a) Hooke’s law region (b) Breaking point

8. A metal plate 5 cm x 5 cm rests on a layer of castor oil 1 mm thick whose coefficient of viscosity is 1.55 Nsm^-2. Find the horizontal force required to move the plate with a speed of 2cms^-1.

9. Eight rains drops of radius 1mm each falling down with terminal velocity of 5 m/s coalesce to form a bigger drop. Find the terminal velocity of the bigger drop.

10. State Stokes’s law. Derive this law by method of dimensions. 

11. State and prove Bernoulli’s theorem.

VALUE POINTS 

1. Modulus of elasticity 

2. This spreads force due to the weight of the train on larger area and hence reduces the pressure considerably.

3. If two streamlines cross each other, there will be two directions of flow at the point of intersection which is impossible.

4. When the two boats come closer to each other, the velocity of water between the narrow gap increases and so pressure decreases. The pressure on the outer surfaces of both the row boats becomes greater than the pressure in the gap. Therefore, the two boats are pulled towards each other.

5. Definition of coefficient of viscosity of a liquid. 

6. Energy density u = ½ x Y x (strain)²
= 2.5 x 104 J/m³
Elastic potential energy U = Energy density x volume
= 0.2 J

7. Stress vs strain graph Representation of (a) Hooke’s law region (b) Breaking point

8. A = 25 x 10^-4 m² , dx = 10^-3 m , η = 1.55 Nsm^-2 , dv = 2 x 10^-2 m/s
F = η A ( dv/dx) substitution of values
F = 0.0775 N

9. Radius of small drop r = 0.1 cm
Terminal velocity v = 5 m/s
Volume of bigger drop = 8 x volume of small drops
4/3 π R³ = 8 x 4/3 π r³
R = 2 rn = 0.2 cm
Terminal velocity of bigger drop
V = v x (R/r)²
V = 20 cm/s

10. Statement of Stokes’s law
Derivation of F = 6πηrv by dimension method

11. Statement of Bernoulli’s theorem Proof with diagram

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