Science (English Medium) कक्षा ११ - CBSE Question Bank Solutions for Physics

If a drop of liquid breaks into smaller droplets, it results in lowering of temperature of the droplets. Let a drop of radius R, break into N small droplets each of radius r. Estimate the drop in temperature.

The sufrace tension and vapour pressure of water at 20°C is 7.28 × 10^–2 Nm^–1 and 2.33 × 10³ Pa, respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at 20°C?

This model of the atmosphere works for relatively small distances. Identify the underlying assumption that limits the model.

Surface tension is exhibited by liquids due to force of attraction between molecules of the liquid. The surface tension decreases with increase in temperature and vanishes at boiling point. Given that the latent heat of vaporisation for water L_v = 540 k cal kg^–1, the mechanical equivalent of heat J = 4.2 J cal^–1, density of water ρ_w = 103 kg l^–1, Avagadro’s No N_A = 6.0 × 1026 k mole^–1 and the molecular weight of water M_A = 18 kg for 1 k mole.

1. Estimate the energy required for one molecule of water to evaporate.
2. Show that the inter–molecular distance for water is `d = [M_A/N_A xx 1/ρ_w]^(1/3)` and find its value.
3. 1 g of water in the vapor state at 1 atm occupies 1601 cm³. Estimate the intermolecular distance at boiling point, in the vapour state.
4. During vaporisation a molecule overcomes a force F, assumed constant, to go from an inter-molecular distance d to d ′. Estimate the value of F.
5. Calculate F/d, which is a measure of the surface tension.

A hot air balloon is a sphere of radius 8 m. The air inside is at a temperature of 60°C. How large a mass can the balloon lift when the outside temperature is 20°C? (Assume air is an ideal gas, R = 8.314 J mole^–1K^–1, 1 atm. = 1.013 × 10⁵ Pa; the membrane tension is 5 Nm^–1.)

Change in temperature of the medium changes ______.

As you have learnt in the text, a geostationary satellite orbits the earth at a height of nearly 36,000 km from the surface of the earth. What is the potential due to earth’s gravity at the site of this satellite? (Take the potential energy at infinity to be zero). Mass of the earth = 6.0 × 10²⁴ kg, radius = 6400 km

The rate of change of total momentum of a many-particle system is proportional to the ______ on the system.

In an inelastic collision of two bodies, the quantities which do not change after the collision are the ______ of the system of two bodies.

State if the following statement is true or false. Give a reason for your answer.

In an elastic collision of two bodies, the momentum and energy of each body is conserved.

State if the following statement is true or false. Give a reason for your answer. 

Total energy of a system is always conserved, no matter what internal and external forces on the body are present.

State if the following statement is true or false. Give a reason for your answer.

In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.

Answer carefully, with reason:

In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact)?

Answer carefully, with reason:

Is the total linear momentum conserved during the short time of an elastic collision of two balls?

Answer carefully, with reason:

In an inelastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e., when they are in contact)?

Answer carefully, with reason:

If the potential energy of two billiard balls depends only on the separation distance between their centres, is the collision elastic or inelastic? (Note, we are talking here of potential energy corresponding to the force during collision, not gravitational potential energy.)

A molecule in a gas container hits a horizontal wall with speed 200 m s^–1 and angle 30° with the normal, and rebounds with the same speed. Is momentum conserved in the collision? Is the collision elastic or inelastic?

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed V. If the collision is elastic, which of the following figure is a possible result after collision?

The bob A of a pendulum released from 30° to the vertical hits another bob B of the same mass at rest on a table, as shown in the figure. How high does the bob A rise after the collision? Neglect the size of the bobs and assume the collision to be elastic.

A bullet of mass 0.012 kg and horizontal speed 70 m s^–1 strikes a block of wood of mass 0.4 kg and instantly comes to rest with respect to the block. The block is suspended from the ceiling by means of thin wires. Calculate the height to which the block rises. Also, estimate the amount of heat produced in the block.