# Class XI Physics Practice Set

Class XI Physics Practice Set

Group: A

1. Answer in brief, any six questions: (6 X 2=12)

a) Prove that the maximum horizontal range is four times the maximum height attained by the projectile when fired at inclination so as to have maximum horizontal range.

b) Why is it difficult to move a cycle with its brakes on?

c) A person carrying bricks on his head on a level road from one place to another is doing no work on the bricks. why?

d) A solid tied at the end of the string is revolved in a vertical circle. At what point the tension in the string is greatest?

e) Why do we say that velocity and acceleration of a body  executing S.H.M. are out of phase?

f) Why does a spring balance used for long time show wrong reading ?

g) Explain why a boat is likely to capsize if persons in the boat stand up ?

2. Answer in brief any two questions. (2x2=4)

a) What is water equivalent. Write its unit.

b) Molecules of different gases have equal K.E. provided their temperature is the same. Do these molecules have equal velocities?

c) If an inflated tyre bursts, the air escaping out is cooled. Why?

3. Answer in brief any one question. (1x2=2)

a) What is the minimum distance between real object and real image in a convex lens ?

b) Why are distant stars not visible to our eyes without a telescope ?

4. Answer in brief any one questions: (1x2=2)

a) What is total charge on 1 kg of electrons?

b) What is the action of dielectric in a capacitor ?

Group B

5. Answer any three questions (3x4=12)

a) Show that there are two angles of projection for which the horizontal range is the same . Also the sum of the maximum heights for these two angles is independent of the angle of projection.

b) Define the centripetal force. Derive an expression for it.

c) What is the kinetic energy of a rotating body? Derive an expression for it.

d) What is capillarity? Derive an expression for rise of a liquid in a capillary tube.

6. Answer any two questions: (2x4=8)

a) State and explain Newton's law of cooling. Describe the method of determining specific heat of liquid.

b) What is meant by a perfect black body? How can you realize such a body in practice?

c) Describe Carnot's heat engine and derive an expression for its efficiency.

7. Answer any one question : (1x4=4)

a) Derive mirror formula for an extended object in case of a concave mirror.

b) Explain the construction and working of a compound microscope. Derive an expression for its magnifying power.

8. Answer any one question : (1x4=4)

a) Derive an expression for the P.E. of a charge at a point in the electric field due to a point charge.

b) Show that the electrical energy is always lost when two conductors at different potentials are connected together.

Group C

9. Solve any three numerical questions. (3x4=12)

a) A ball is dropped from a height of 20m and rebounds with a velocity which is 3/4 of the velocity with which it hits the ground. What is the time interval between the first and second bounces.

b) A stationary mass explodes into two parts of mass 4 units and 40 units respectively. If the larger mass has an initial Kinetic energy of 100 J, what is the initial Kinetic energy of the smaller mass?

c) The time period of a body executing S.H.M. is 2S. After how much time from the instant at t=0, its displacement will be half of the amplitude?

d) Two drops of some liquid of same radius are falling through air with steady velocity of 1.5 cms-1. If two drops coalesce, what would be the terminal velocity?

10. Solve any two numerical questions: (3x2 = 6)

a) A steel wire 8 metre long and 4 mm in diameter is fixed to two rigid supports. Calculate the increase in tension when the temperature falls by 100C. [Linear expansivity of steel = 12 X 10-6 K-1, Young's modules for steel = 2 X 1011 Nm-2]

b) The volume of the gas is 1 litre, pressure is 1.2 X 107 Nm-2 and the temperature 400 K. Find the number of molecules in the gas. (Boltzman Constant K = 1.38 X 10-23 JK-1).

c) A quantity of mono-atomic gas at 270C is compressed (i) slowly and (ii) suddenly to 8/27 of its volume. Find the change in temperature in each case, assuming  to be 5/3.

11. A ray of light travelling in water is incident at an angle of 300C on a water glass interface. Calculate the angle of refraction. (Refractive index of water is 4/3 and for glass is 3/2). (4)

12. A metallic sphere of radius 2m is charged in air to a potential of 3000 V. Calculate the energy stored in the sphere. (3)