#### Public Exam Model Question Paper 2019 - 2020

11th Standard

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Physics

Time : 02:45:00 Hrs
Total Marks : 70

Part I

Answer all the questions.

Choose the most suitable answer from the given four alternatives and write the option code with the corresponding answer.

15 x 1 = 15
1. How many AU present in one light year?

(a)

6.30 x 104m

(b)

9.46 x 1015m

(c)

6.2 x 102m

(d)

9.4 x 1016m

2. Two objects of masses m1 and m2 fall from the heights h1 and h2 respectively. The ratio of the magnitude of their momenta when they hit the ground is

(a)

$\sqrt { \frac { { h }_{ 1 } }{ { h }_{ 2 } } }$

(b)

$\sqrt { \frac { { { m }_{ 1 }h }_{ 1 } }{ { { m }_{ 2 }h }_{ 2 } } }$

(c)

$\frac { { m }_{ 1 } }{ { m }_{ 2 } } \sqrt { \frac { { h }_{ 1 } }{ { h }_{ 2 } } }$

(d)

$\frac { { m }_{ 1 } }{ { m }_{ 2 } }$

3. $\hat i\times \hat j$ is

(a)

$\hat i$

(b)

$\hat j$

(c)

$\hat k$

(d)

$\vec z$

4. Choose appropriate free body diagram for the particle experiencing net acceleration along negative y direction. (Each arrow mark represents the force acting on the system).

(a)

(b)

(c)

(d)

5. An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of 12 ms-1 and the second part of mass 2 kg moves with 8 ms-1 speed. If the third part flies off with 4 ms-1 speed, then its mass is

(a)

7 kg

(b)

17 kg

(c)

3 kg

(d)

5 kg

6. If kinetic energy of a body is increased by 300% then percentage change in momentum will be

(a)

100%

(b)

150%

(c)

265%

(d)

73.2%.

7. The ratio of the acceleration for a solid sphere (mass m and radius R) rolling down an incline of angle $\theta$ without slipping and slipping down the incline without rolling is,

(a)

5 : 7

(b)

2: 3

(c)

2: 5

(d)

7: 5

8. A circular disc is rolling down in an inclined plane without slipping. The percentage of rotational energy in its total energy is

(a)

66.61%

(b)

33.33%

(c)

22.22%

(d)

50%

9. The time period of a satellite orbiting Earth in a cirular orbit is independent of.

(a)

Radius of the orbit

(b)

The mass of the satellite

(c)

Both the mass and radius of the orbit

(d)

Neither the mass nor the radius of its orbit

10. Which of the following statement about the gravitational constant is true?

(a)

It is a force

(b)

It has same value in all system of unit

(c)

It has not unit

(d)

It depends on the value of the masses

11. A certain number of spherical drops of a liquid of radius R coalesce to form a single drop of radius R and volume V. If T is the surface tension of the liquid, then

(a)

energy = 4 V T $\left( \frac { 1 }{ r } -\frac { 1 }{ R } \right)$is released

(b)

energy = 3 V T $\left( \frac { 1 }{ r } -\frac { 1 }{ R } \right)$is absorbed

(c)

energy = 3 V T $\left( \frac { 1 }{ r } -\frac { 1 }{ R } \right)$is released

(d)

energy is neither released nor absorbed

12.  A mono atomic gas is suddenly compressed to $\left( \frac { 1 }{ 8 } \right) ^{ th }$ its initial volume adiabatically the ratio of its final pressure to the intial pressure is (Given: the ratio of +!le =peclfier heats of the given gas to be 5/3)

(a)

32

(b)

$\frac { 40 }{ 3 }$

(c)

$\frac { 24 }{ 5 }$

(d)

8

13. The mean translational K.E. of a perfect gas molecule at absolute temperature T is (K is Boltzmann constant)

(a)

$\frac{1}{2}$kT

(b)

kT

(c)

$\frac{3}{2}$kT

(d)

$\frac{5}{2}$kT

14. Which of the following differential equations represents a damped harmonic oscillator?

(a)

$\frac { { d }^{ 2 }y }{ { dt }^{ 2 } } +y=0$

(b)

$\frac { { d }^{ 2 }y }{ { dt }^{ 2 } } +\gamma \frac { dy }{ d } +y=0$

(c)

$\frac { { d }^{ 2 }y }{ { dt }^{ 2 } } +{ k }^{ 2 }+y=0$

(d)

$\frac { dy }{ d } +y=0$

15. Compare the velocities of the wave forms given below, and choose the correct option.

where, vA, vB, vC and vD are velocities given in (A), (B), (C) and (D), respectively.

(a)

vA > vB > vD > vC

(b)

vA< vB < vD < vC

(c)

vA = vB = vD = vC

(d)

vA > vB = vD > vC

16. Part II

Answer any 6 questions. Question no. 24 is compulsory.

6 x 2 = 12
17. Define one second.

18. Two bodies of masses 15 kg and 10 kg are connected with light string kept on a smooth surface. A horizontal force F=500 N is applied to a 15 kg as shown in the figure. Calculate the tension acting in the string

19. When a tree is cut, the cut is made on the side facing the direction in which the tree is required to fall. Why?

20. State the theory of geocentric model of solar system? And by whom this was proposed.

21. What are the physical states of matter?

22. What is meant by conduction?

23. Calculate the mean free path of air molecules at STP. The diameter of N2 and O2 is about 3 × 10-10 m

24. Classify the following motions as periodic and non-periodic motions?.
a. Motion of Halley’s comet.
b. Motion of clouds.
c. Moon revolving around the Earth

25. The fundamental frequency in an open organ pipe is equal to the 3rd harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm. What is the length of the open organ pipe.

26. Part III

Answer any 6 questions. Question no. 33 is compulsory.

6 x 3 = 18
27. A particle moves along the x-axis in such a way that its coordinates x varies with time 't' according to the equation x = 2 - 5t + 6t2. What is the initial velocity of the particle?

28. When a cricket player catches the ball, he pulls his hands gradually in the direction of the ball's motion. Why?

29. Compute the work done by the gravitational force for the following cases

30. Find the moment of inertia of a uniform rod about an axis which is perpendicular to the rod and touches anyone end of the rod.

31. The following photographs are taken from the recent lunar eclipse which occurred on January 31, 2018. Is it possible to prove that Earth is a sphere from these photographs?

32. Stress - Strain curve for two wires of material A and B are as shown in figure.

(a) Which material in more ductile?
(b) Which material has greater value of young's modulus?
(c) Which of the two is stronger material?
(d) Which material is more brittle?

33. 500 g of water is heated from 30°C to 60°C. Ignoring the slight expansion of water, calculate the change in internal energy of the water? (specific heat of water 4184 J/kg.K)

34. Derive the expression of pressure exerted by the gas on the walls of the container.

35. Derive the Equation of a plane progressive wave.

36. Part IV

Answer all the questions.

5 x 5 = 25
1. Explain with graphs the difference between work done by a constant force and by a variable force

2. A transverse harmonic wave on a string is described by y(x, t) =5.0 sin (48t + 0.0264x + ), where x and yare in em and t in sec. The positive direction of x is from left to right.
(a) What are its amplitude and frequency?
(b) What is the least distance between two success in crests in the wave?

1. Derive the expression for gravitational potential energy.

2. State Hooke’s law and verify it with the help of an experiment.

1. Distinguish between isothermal and adlabatlc process.

2. Ten particles are moving at the speed of 2, 3, 4, 5, 5, 5, 6, 6, 7 and 9 m s-1. Calculate rms speed, average speed and most probable speed.

1. A three storey building of height 100m is located on Earth and a similar building is also located on Moon. If two people jump from the top of these buildings on Earth and Moon simultaneously, when will they reach the ground and at what speed? (g = 10m s-2)

2. Show that for a simple harmonic motion, the phase difference between
a. displacement and velocity is $\frac{\pi}{2}$radian or 90°.
b. velocity and acceleration is  $\frac{\pi}{2}$radian or 90°.
c. displacement and acceleration is $\pi$  radian or 180°.

1. Briefly explain the origin of friction. Show that in an inclined plane, angle of friction is equal to angle of repose

2. The moment of inertia of a thin rod of mass 'M' and length 'I' about an axis passing through its centre is $\frac { M{ l }^{ 2 } }{ 12 }$. Calculate the moment of inertia about a parallel axis through end of rod.