PUC Science Class 11 - Karnataka Board PUC Question Bank Solutions

A hot liquid is kept in a big room. Its temperature is plotted as a function of time. Which of the following curves may represent the plot?

50 cc of oxygen is collected in an inverted gas jar over water. The atmospheric pressure is 99.4 kPa and the room temperature is 27°C. The water level in the jar is same as the level outside. The saturation vapour pressure at 27°C is 3.4 kPa. Calculate the number of moles of oxygen collected in the jar.

A 100 W bulb has tungsten filament of total length 1.0 m and radius 4 × 10⁻⁵ m. The emissivity of the filament is 0.8 and σ = 6.0 × 10⁻⁸ W m⁻²K⁴. Calculate the temperature of the filament when the bulb is operating at correct wattage.

A spherical tungsten piece of radius 1.0 cm is suspended in an evacuated chamber maintained at 300 K. The piece is maintained at 1000 K by heating it electrically. Find the rate at which the electrical energy must be supplied. The emissivity of tungsten is 0.30 and the Stefan constant σ is 6.0 × 10⁻⁸ W m⁻² K⁻⁴.

Some washing machines have cloth driers. It contains a drum in which wet clothes are kept. As the drum rotates, the water particles get separated from the cloth. The general description of this action is that "the centrifugal force throws the water particles away from the drum". Comment on this statement from the viewpoint of an observer rotating with the drum and the observer who is washing the clothes.

A small coin is placed on a record rotating at \[33\frac{1}{3}\] rev/minute. The coin does not slip on the record. Where does it get the required centripetal force from ?

After a good meal at a party you wash your hands and find that you have forgotten to bring your handkerchief. You shake your hand vigorously to remove the water as much as you can. Why is water removed in this process?

Consider the circular motion of the Earth around the sun. Which of the following statements is more appropriate?

(a) Gravitational attraction of the sun on the earth is equal to the centripetal force.
(b) The gravitational attraction of the sun on the earth is the centripetal force.

A heavy mass m is hanging from a string in equilibrium without breaking it. When this same mass is set into oscillation, the string breaks. Explain. 

A particle of mass m is observed from an inertial frame of reference and is found to move in a circle of radius r with a uniform speed v. The centrifugal force on it is 

A particle of mass m rotates with a uniform angular speed ω. It is viewed from a frame rotating about the Z-axis with a uniform angular speed ω₀. The centrifugal force on the particle is 

A bob suspended from the ceiling of a car which is accelerating on a horizontal road. The bob stays at rest with respect to the car with the string making an angle θ with the vertical. The linear momentum of the bob as seen from the road is increasing with time. Is it a violation of conservation of linear momentum? If not, where is the external force changes the linear momentum?

Two bodies make an elastic head-on collision on a smooth horizontal table kept in a car. Do you expect a change in the result if the car is accelerated in a horizontal road because of the non inertial character of the frame? Does the equation "Velocity of separation = Velocity of approach" remain valid in an accelerating car? Does the equation "final momentum = initial momentum" remain valid in the accelerating car?

A person applies constant force \[\overrightarrow{\text{F}}\]on a particle of mass m and finds that the particle moves in a circle of radius r with a uniform speed v as seen from an inertial frame of reference. 

(a) This is not possible.
(b) There are other forces on the particle.
(c) The resultant of the other forces is \[\frac{\text{mv}^2}{\text{r}}\] towards the centre.

d) The resultant of the other forces varies in magnitude as well as in direction

If the total mechanical energy of a particle is zero, is its linear momentum necessarily zero? Is it necessarily nonzero?

If the linear momentum of a particle is known, can you find its kinetic energy? If the kinetic energy of a particle is know can you find its linear momentum?

Suppose we define a quantity 'Linear momentum' as linear momentum = mass × speed.
The linear momentum of a system of particles is the sum of linear momenta of the individual particles. Can we state principle of conservation of linear momentum as "linear momentum of a system remains constant if no external force acts on it"?

In the Bohr model of hydrogen atom, the electron is treated as a particle going in a circle with the centre at the proton. The proton itself is assumed to be fixed in an inertial frame. The centripetal force is provided by the Coulomb attraction. In the ground state, the electron goes round the proton in a circle of radius 5.3 × 10⁻¹¹ m. Find the speed of the electron in the ground state. Mass of the electron = 9.1 × 10⁻³¹ kg and charge of the electron = 1.6 × 10⁻¹⁹ C.