Tuesday, 2 January 2018


Class XI Physics
Time: 3 hours                                                                                  Maximum Marks: 70
General Instructions:
(i) All questions are compulsory. There are 26 questions in all.
(ii) This question paper has five sections: Section A, Section B, Section, Section D and
Section E.
(iii) Section A contains five questions of one mark each, section B contains five questions
of two marks each, section C contains twelve questions of three marks each, section
D contains one value based question of four marks and section E contains three
questions of five marks each.
(iv) There is no overall choice. However, an internal choice has been provided in one
question of two marks, one question of three marks and all the three questions of five
marks weightage. You have to attempt only one of the choices in such questions.

1. Lubricants are used between the two parts of a machine. Why ?.
2. Where is the centre of mass of a meter stick?
3. Why does a gun recoils when a bullet is being fired ?
4. Why is it difficult to catch a cricket ball than a tennis ball even when both
are moving with the same velocity ?
5. Which spring has greater value of spring constant – a hard spring or a delicate
spring ?
6. Define angle of friction and angle of repose.
 7. Why does a speedy motor cyclist bends towards the centre of a circular path
    while taking a turn on it ?
 8. The outer edge of a curved road is generally raised over the inner edge.
 9. Two springs A and B are identical except that A is harder than B (KA > KB) if these are
   stretched by the equal force. In which spring will more work be done ?
 10. How much work is done by a railway porter walking on a horizontal platform with
    a load on his head ? Explain.OR
Explain that gravitational force is a conservative force.

11. Derive  the expression for rotational kinetic energy of a rigid body rotates with angular velocity ѡ and moment of Inertia I.

12. How high must a body be lifted to gain an amount of P.E. equal to the K.E. it has when
     moving at speed 20 ms–1. (The value of acceleration due to gravity at a place is 9.8 ms–2).
13. State and prove work energy theorem.
14. 20 J work is required to stretch a spring through 0.1 m. Find the force constant of the spring.
     If the spring is further stretched through 0.1 m. Calculate work done.
15. A spring balance is attached to the ceiling of a lift. When the lift is at rest
spring balance reads 49 N of a body hang on it. If the lift moves :
(i) Downward
(ii) upward, with an acceleration of 5 ms–2
(iii) with a constant velocity.
What will be the reading of the balance in each case ?

16. A block placed on a rough horizontal surface is pulled by a horizontal force
F. Let f be the force applied by the rough surface on the block. Plot a graph
of f versus F.
17. A block slides down as incline of 30° with the horizontal. Starting from rest, it covers 8 m in the first 2 seconds. Find the coefficient of static friction.
8. Derive an expression for K.E. of a body of mass ‘m’ moving with velocity ‘v’ by calculus method.
18. Give the physical significance of moment of inertia. Explain the need of fly wheel in Engine.
19. Three masses 3 kg, 4 kg and 5 kg are located at the corners of an equilateral triangle of side 1 m. Locate the centre of mass of the system.
20. What is the turning effect of force called for ? On what factors does it depend ?
21.What do you mean by Radius of  gyration? Derive the expression for Radius of gyration.

22 .A truck of mass 1000 kg accelerates uniformly from rest to a velocity ofs–1 in 5 seconds. Calculate (i) its acceleration, (ii) its gain in K.E.,

Suresh noticed a big Granite Rock in his locality. He thought that if they worked upon it they could earn money. He took permission from the Government, completed all the formalities .He broke the Rock using a bomb. The rock was made into slices .They established a Granite industry. Many of the people in the surroundings started to earn and live comfortably. (a) What values of Suresh impress you? (b)A bomb is thrown in a horizontal direction with a velocity of 50 m/s. It explodes into two parts of masses 6 Kg and 3 Kg. the heavier fragment continues to move in the horizontal direction with a velocity of 80 m/s .Calculate the velocity of the lighter fragment.


24.Show that at any instant of time during the motion total mechanical energy
     of a freely falling body remains constant. Show graphically the variation of K.E. and P.E.
    during the motion.
25.How does a perfectly inelastic collision differ from perfectly elastic collision? Two particles
   of mass m1 and m2 having velocities U1 and U2 respectively make a head on collision. Derive
    the relation for their final velocities. Discuss the following special cases.
    (i) m1 = m2
    (ii) m1 >> m2 and U2 = 0
    (iii) m1 << m2 and U1 = 0
    Define spring constant, write the characteristics of the force during the elongation of a spring.
    Derive the relation for the P.E. stored when it is elongated by X. Draw the graphs to show the
    variation of P.E. and force with elongation.

26. With the help of suitable example, explain the terms static friction, limiting friction and
       kinetic  friction. Show that static friction is a self adjustingforce.
    a)State Newton’s Second law
       There are few forces acting at a Point P produced by strings as shawn,which is at rest, Find
       the forces F1 & F2