#### CBSE Sample Paper 2020-21 Physics (042) for class 11

Class-XI

Time allowed :3:00 hours

Maximum Marks:70

General Instructions:

All questions are compulsory. Section A contains 20 questions of 1 mark each. Section B contains 7 questions of 2 marks each. Section C contains 7 questions of 3 marks each. Section D contains 3 questions of 5 marks each.

**Section -A**

- Precision of measurement depends on
- Least count of measuring instrument.
- Temperature of the surroundings
- Carefulness of observer
- All of the above
- For a given change in linear momentum when time of impact increases , force
- Increases
- Remains same.
- None of the above
- When the surfaces in contact are made too smooth by polishing force of friction is
- Decreases
- Increases
- becomes zero
- becomes infinite
- The linear momentum of a body is increased by 10%. What is the percentage increase in kinetic energy?
- 10%. (b) 20%. (c) 21%. (d) none of the above
- What would be the length of the day if earth were to shrink suddenly to 1/64
^{th}of its original volume? - 24 h (b) 12 h (c) 6 h (d) 1.5 h
- At what depth below the surface of earth the value of g is same as that at a height of 5 kilometre?
- 10 km (b) 7.5 km (c) 5 km d) 2.5 km
- It is observed that during a storm the roof of a house are blown off.It is because-
- The wind creates high pressure over the roof
- The wind creates low pressure over the roof
- Of the structure and shape of the roof
- Of natural calamity
- A wire can support a load Mg without breaking. It is cut into two equal parts the maximum load that each part can support is
- Mg/4 (b) Mg/2 (c) Mg (d) 2Mg
- Internal energy of an ideal gas depends upon
- volume only
- temperature only
- both, volume and temperature
- Neither volume nor temperature
- The mean kinetic energy per unit volume of gas is related to average pressure exerted by the gas is
- E=2/3P (b) 3/2P (c) E=P (d) E= 5/4P
- Average straight distance covered between two successive collisions of molecule is called______________.
- Melting process and boiling process are______________.
- Amount of heat required to raise the temperature of unit mass of substance through unit degree is called____________ of the substance.
- The value of acceleration due to gravity is______________ everywhere on the surface of Earth.
- Moment of inertia of a uniform circular ring of mass M and radius R about a diameter of ring is______________.
- Name any two dimensional constants.
- Rubber tyres are preferred to steel Tyres. Why?
- Does sun do any work on Earth, When Earth revolve around the sun in a perfectly circular orbit?
- Name the rotational analogue of force what is its unit?
- What are the two theorems of moment of inertia?

**Section-B**

- What do you understand by escape velocity? Derive an expression for it in terms of parameters of given planet.
- Why are the bridges declared unsafe after long use?
- Mercury does not cling to glass. Why?
- Obtain an expression for work done by a gas in an isothermal expansion.
- Explain Boyle’s law and Charle’s law.
- What is the moment of inertia of a ring about a tangent to the circle in the plane of the ring?
- State and establish principle of conservation of energy.

**Section C**

- A sphere of aluminum of mass 0.047 kg placed for sufficient time in a vessel containing boiling water, so that the sphere is at 100°C.It is then immediately transferred to 0.14 Kg copper calorimeter containing 0.25 kg of water at 20°C.The temperature of water rises and attains a steady State at 23°C. Calculate the specific heat capacity of aluminum. Specific heat capacity of copper=0.386×103 J/kg K. Specific heat capacity of water=4.18×103 J/kg K.
- Uranium has two isotopes of masses 235 and 238 units. If both are present in uranium hexa fluoride gas, which would have the larger average speed? If atomic mass of fluorine is 19 units, estimate the percentage difference in speeds at any temperature.
- Discuss the bending of cyclist while describing a curved path find the relation for angle of bending of the cyclist.

Or

Explain gravitational potential at a point and gravitational potential energy of a body in a gravitational field . establish a relation between them.

- Explain what is meant by potential energy of a spring? Obtain an expression for it and discuss the nature of its variation.
- State Pascal law. Give the construction and working of hydraulic lift.
- What is meant by degrees of freedom? State law of equipartition of energy. Hence calculate specific heat of mono di and triatomic gases.

Or

Explain surface energy .established its relation which surface tension.

- Obtain an expression for kinetic energy of rotation of a body. Hence define moment of inertia of the body explain its physical significance.

Or

Two identical billiard ball strikes a rigid wall with the same speed but at different angles and get reflected without any change in speed as shown in figure. what is the direction of the force on the wall due to each one and the ratio of the magnitude of impulse imparted to the balls by the wall.

- Find an expression for the pressure exerted by gas and establish its relation with kinetic energy of the gas.

**Section –D**

**D**escribe Carnot cycle and derive an expression for efficiency of this cycle.- State and prove Bernoulli’s theorem. Give two practical applications of Bernoulli’s theorem.
- Discuss the principle of launching of a satellite and explain what you understand by geostationary satellites. Mention the essential conditions for geostationary satellite.

Or

Discuss elastic collision in one dimension .obtain expression for velocities of the two bodies after such a collisions.