NBSE Class 11 Question Paper 2021 for Physics

Total number of printed pages : 4 NB/XI/PHY/1

2021
PHYSICS
Total marks : 70 Time : 3 hours

General instructions:
i) Approximately 15 minutes is allotted to read the question paper and revise the
answers.
ii) The question paper consists of 30 questions. All questions are compulsory.
iii) Marks are indicated against each question.
iv) Internal choice has been provided in some questions.
N.B: Check that all pages of the question paper is complete as indicated on the top left side.

1. The dimensional formula of impulse is 1
(a) [MLT ˉ1] (b) [MLT ˉ2]
1 2
(c) [ML ˉ T ˉ ] (d) [ML ˉ1 T ˉ1]
2. A particle is said to be in equilibrium if the net external force on the
particle is 1
(a) zero (b) constant
(c) positive (d) negative

3. A couple produces 1
(a) purely rotational motion
(b) purely linear motion
(c) linear and rotational motion
(d) no motion
4. The relation connecting Kelvin temperature (T) and Celsius
temperature(tc) is 1
(a) T= tc + 273 (b) T= tc − 273
(c) T= tc + 373 (d) T= tc − 373

5. Which of the following does not represent a simple harmonic motion? 1
(a) y= a sin t (b) y= a cos t
(c) y= a sin t + b cos t (d) y= a tan t

6. What is static friction? 1

7. Show that the vectors A= iˆ  2 ˆj  4kˆ and B= 2iˆ − ĵ are perpendicular. 1

8. What is a geostationary satellite? What is its time period? 1

9. State Hooke’s law. 1

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10. On what factors does the angular frequency of a simple harmonic
motion depend upon? 1

11. a. A car is moving along a straight line say OP. It moves from O to P
in 18s. If the distance from O to P is 360m, what will be the average
velocity and average speed of the car in going from O to P.
Or 2
b. The position of an object moving along x-axis is given
by x= a + bt2 where a = 8.5m, b = 2.5ms−2 and t is measured in
seconds. What is its velocity at t = 0s and t = 2.0s?

12. a. Differentiate between exothermic and endothermic reaction.
Or 2
b. State and prove the work-energy theorem for a variable force.

13. Find the torque of a force 7iˆ  3 ˆj  5kˆ about the origin. The force
acts on a particle whose position vector is iˆ  ˆj  kˆ . 2

14 What is central force? On what factors does the magnitude of central
force depend on? 2

15. a. State second law of thermodynamics in its two usual forms.
Or 2
b. Prove that the specific heat of solids are given by the formula
C=3R, where R is the universal gas constant.

16. Define mean free path. Write its mathematical expression. 2

17. Consider a simple pendulum, having a bob attached to a string, that
oscillates under the action of the force of gravity. Suppose that the
period of oscillation of the simple pendulum depends on its length (l),
mass of the bob (m) and acceleration due to gravity (g). Derive an
expression for its time period using method of dimensions. 3

18. Draw the position-time graphs for two objects A & B with
a) equal velocities
b) unequal velocities
c) opposite velocities. 3

19. Derive an expression for maximum velocity of a car while moving
on a banked road. 3

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20. a. What is friction? Explain why is friction a necessary evil.
Or 3
b. What is centripetal acceleration? Derive an expression for the
centripetal force of a body moving in a circular path of radius ‘r’
with a uniform speed ‘v’.

21. a. Show that the total mechanical energy of a system is conserved if
the forces doing work on it are conservative.
Or 3
b. Two bodies A & B having masses m1 & m2 moving with v1 & v2
velocities undergoes completely inelastic collision. Show that the
heavier mass (m2) is undisturbed while the lighter mass (m1) reverses
its velocity.

22. a. Derive a relation between the angular velocity and linear velocity.
Or 3
b. Prove that the total momentum of a system of particle is equal to
the product of the total mass of the system and the velocity of
centre of mass.

RE
23. a. Show that To = 2 where RE is radius of the earth.
g
Or 3

b. Show that (Vi)min = 2 gRE where (Vi)min is the escape speed of
satellite.

24. Explain the stress – strain curve of a metal wire with the help of a
suitable diagram. 3

25. Derive an expression for the work done during an isothermal process. 3

1
26. Prove that the pressure exerted by an ideal gas is P =  2 where 
3
is the density of the gas and  2 is the mean square speed of gas
molecules. 3

27. Define frequency. Write the formula in terms of time period. What is
its S.I unit? 3

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28. a. A projectile is projected with a velocity ‘v’ making an angle ‘  ’
with the horizontal. Show that path followed by the projectile is
parabolic. Find the expression for time of flight, maximum height and
horizontal range.
Or 5
b. What is average acceleration? Obtain an expression for the motion
in a plane with constant acceleration.

29. a. State and prove Bernoulli’s principle.
Or 5
b. What is venturimeter? Derive an expression for the speed of fluid
with the help of a schematic diagram.

30. a. Define displacement. Establish the relation D = A 2  B 2 , and
write the importance of periodic sine and cosine functions.

Or 5

b. Derive the expression for the total energy for a particle executing
simple harmonic motion.

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