### CBSE Board Physics Class XI | Sample Paper -1 |

### Class-XI

### Time: 3 hour

#### Subject- Physics M.M.-80

All questions are compulsory.

Section A

- Why do we not consider rate of change of acceleration in the study of linear motion.
- A projectile is fired with kinetic energy 1kj. If the range is maximum what is its K.E. at the highest point?
- Rocket can move in air free space but jet planes cannot .Why?
- A spring of force constant K is cut into pieces of lengths l
_{1 }and l Calculate force constant of each part? - A particle performs uniform circular motion with an angular momentum L. If the frequency of particle’s motion is doubled and its K.E. is halved, what happens to its angular momentum?

Section B

- Can centre mass of a body coincide with the geometrical centre of the body?
- A constant torque is acting on a wheel .If starting from rest; the wheel makes n rotations in t seconds. Find the acceleration?
- What is the minimum energy released in the annihilation of an electron positron pair?
- A light body and a heavy body have same kinetic energy. Which one has greater linear momentum?
- A force F is related to the position of a particle by the relation F=(10x
^{2 })N find the work done by the force when the particle moves from x=2 m to x=4m

Section C

- Finding dimensions of resistance R and inductance L, Speculate what physical quantities (L/R) and L I
^{2 }represent, where I is current? - Add 6.75 ×10
^{3 }cm to 4.52 ×10^{2 }cm? - Three particles A, B and C are situated at the vertices of an equilateral triangle ABC of sides a t=0. Each of the particles move with constant speed v. A always has its velocity along AB, B along BC and C along CA. At what time will these particles meet each other?
- A body travels a distance of 2m in 2sec and 2.2 m in next 4 sec what will be the velocity of the body at the end of 7
^{th}second from the start. - If the magnitude of vectors A, B and C are 3, 4, 5 units respectable and if A+B=c, find the angel between A and C.
- Find the angel of projection for a projectile motion whose range R is n times the maximum height H.
- A rocket of initial mass 6000 kg ijects mass at a constant rate of 16km/sec with constant relative speed of 11m/sec what is the acceleration of the rocket one minute after blast ?
- Find the angel through which a cyclist bends when he covers a circular path 34.3 m long in √22 sec. Given g= 9.8 m/s
^{2}. - A body of mass M at rest struck by a moving body of mass m. Prove that the friction of the initial kinetic energy of mass transferred to the struck body is .
- A light body and a heavy body have same linear momentum. Which one has greater K.E
- The spin drier of a washing machine revolving at 15rps slows down to 5rps while making 50 revolutions find (a) angular acceleration and b time taken.
- What is the moment of inertia of a road of mass M, length about an axis perpendicular to it passing through one of its ends?

Section D

- The concept of centre mass proves that laws of mechanics which are true for appoints mass, are equally valid for all macroscopic bodies of any shape, size, mass etc. for example when vector some of external forces acting on a system of particles zero, the velocity of centre of mass of the system will remain constant.

Read the above passage and answer the following questions.

- Is centre of mass of a body real point
- Does center of mass lie within the body always

- How do you justify that V cm = constant

- (i) State and prove theorem of parallel axes

(ii)state and prove theorem of perpendicular axes

- (i) Discuss rolling without slipping of a cylinder down a rough inclined plain and obtained and expression for the coefficient of friction necessary for the same.

(ii) Three bodies, a ring a solid cylinder and a solid sphere roll down the same inclined plane without slipping. They start from rest. The radii of the bodies are identical which of the bodies reaches the ground with maximum velocity.

- A spare of mass m moving with velocity u hits another stationary sphere of same mass. If e is coefficient of restitution, what is the ratio of velocities of to spheres after collision?