Central Board of Secondary Education (CBSE)

**Sample Paper – 2012**

**Class – XI**

**Subject – Physics**

1. Write the Name a pair of physical quantities which have dimensions **M L ^{2} T^{-1}**.

2. Define physical quantity which has unit but no dimension.

3. The speed of an object can never be negative. What is reason behind it?

4. Draw a suitable graph for uniform motion given by **X=Xo + v t.**

5. Can we add velocity vector to a displacement vector? If no, mention reason?

6. Explain about the nature of motion of an object falling freely under the action of gravity?

7. Is it possible to shield a body from gravitational effect?

8. Velocity of flow of water in a horizontal pipe is 10 ms^{-1}.Find the velocity head of water.

9. A body starts from rest and travels 120 cm in the sixth sec. Calculate the acceleration in the body.

10. The horizontal range of the projectile is 2√3 times its maximum height .Find the angle of projection.

11. Compute the least acceleration with which a 45 kg man slides down a rope if the rope can withstand a tension of 300 N.

12. A ball of mass 150 g moving with a speed of 20 m/s is turned back at the same speed by a player. Calculate the impulse of force.

13. At what height above the surface of the earth will the value of **g** be reduced to **g/4**?

**OR**

Show that the moon would escape for ever from its orbit if its speed were increased by 41.4 %.

14. Different planets have different escape velocities. Why?

15. What force is required to stretch a steel wire of 1 cm^{2} cross section to double its length?( Y=2×10^{11 }Nm^{-2 })

16. Explain Stoke’s law.

17.State:-

(i) Second law of thermodynamics.

(ii)Newton’s law of cooling.

18. Find the time period of a simple pendulum of length 250 cm.

19. The time of oscillation of a small drop of liquid under surface tension depends upon the density **ρ**, radius **a** and surface tension **T**. Using dimensional analysis prove that the period of oscillation **t α √ ρa ^{3}/T.**

** **20. A ball is thrown from a bridge 122.5 m high. After the first ball has fallen for 2 sec, a second ball is thrown straight down after it. What must be the initial velocity of the second ball, so that both the balls hit the surface of water at the same time?

21. State and prove the law of conservation of linear momentum. Name the principle used in rocket propulsion.

22. Find the value **λ** of so that the vectors **A=2 i +j+ λk** and **B=2i-4j+2k** are perpendicular to each other.

**OR**

If **A+B=C** and **A ^{2}+B^{2}=C^{2}** then prove that A and B are perpendicular to each other.

23.Two ball bearing of mass **m** each moving in opposite direction with equal speed **v **collide head on with each other .Predict the out come of the collision, assuming it to be perfectly elastic.

24. Show that the angular momentum of a satellite of mass **Ms** revolving around earth of mass **Me** in an orbit of radius **r** is √**G Ms ^{2} Me r.**

25. Three mass points **m _{1}**,

**m**and

_{2}**m**are located at the vertices of an equilateral triangle of length

_{3}**a**. What is the moment of inertia of the system about an axis along the altitude of the triangle passing the

**m**?

_{1}26.What is Reynolds number? Calculate Reynolds number for water flowing in a tube of radius 0.5 cm with an average velocity of 10 cm/ s.Take η_{w}=10^{-3} kg m^{-1}s^{-1} ρ_{w}=10^{3} kg m^{-3}.

27. At what temperature, if any, do the following pairs of scales give the same reading?

(i) Celsius and Fahrenheit

(ii) Kelvin and Celsius.

28. Discuss the construction and working of heat engine **or** refrigerator. Calculate the efficiency of the Carnot’s engine working between the steam point and the ice point.

29. Define SHM .State its characteristics. Derive an experiment for velocity and acceleration of a particle executing SHM.

**OR**

Derive an expression for k.e. and p.e. of a particle performing SHM and show that energy of particle at any instant of time does not depend on time.

30. Discuss Doppler’s effect in sound.

**OR**

Show that in a closed organ pipe only odd harmonics can be produced.