PUC Science Class 11 - Karnataka Board PUC Question Bank Solutions

A brick weighing 4.0 kg is dropped into a 1.0 m deep river from a height of 2.0 m. Assuming that 80% of the gravitational potential energy is finally converted into thermal energy, find this thermal energy is calorie.

A van of mass 1500 kg travelling at a speed of 54 km h⁻¹ is stopped in 10 s. Assuming that all the mechanical energy lost appears as thermal energy in the brake mechanism, find the average rate of production of thermal energy is cal s⁻¹.

A block of mass 100 g slides on a rough horizontal surface. If the speed of the block decreases from 10 m s⁻¹ to 5 m s⁻¹, find the thermal energy developed in the process.

The blocks of masses 10 kg and 20 kg moving at speeds of 10 m s⁻¹ and 20 m s⁻¹respectively in opposite directions, approach each other and collide. If the collision is completely inelastic, find the thermal energy developed in the process.

The thermal conductivity of a rod depends on

One end of a metal rod is kept in a furnace. In steady state, the temperature of the rod

A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly

A piece of charcoal and a piece of shining steel of the same surface area are kept for a long time in an open lawn in bright sun.
(a) The steel will absorb more heat than the charcoal
(b) The temperature of the steel will be higher than that of the charcoal
(c) If both are picked up by bare hand, the steel will be felt hotter than the charcoal
(d) If the two are picked up from the lawn and kept in a cold chamber, the charcoal will lose heat at a faster rate than the steel.

A uniform slab of dimension 10 cm × 10 cm × 1 cm is kept between two heat reservoirs at temperatures 10°C and 90°C. The larger surface areas touch the reservoirs. The thermal conductivity of the material is 0.80 W m⁻¹ °C⁻¹. Find the amount of heat flowing through the slab per minute.

A liquid-nitrogen container is made of a 1 cm thick styrofoam sheet having thermal conductivity 0.025 J s⁻¹ m⁻¹ °C⁻¹. Liquid nitrogen at 80 K is kept in it. A total area of 0.80 m² is in contact with the liquid nitrogen. The atmospheric temperature us 300 K. Calculate the rate of heat flow from the atmosphere to the liquid nitrogen.

Water is boiled in a container having a bottom of surface area 25 cm², thickness 1.0 mm and thermal conductivity 50 W m⁻¹°C⁻¹. 100 g of water is converted into steam per minute in the steady state after the boiling starts. Assuming that no heat is lost to the atmosphere, calculate the temperature of the lower surface of the bottom. Latent heat of vaporisation of water = 2.26 × 10⁶ J kg⁻¹.

A icebox almost completely filled with ice at 0°C is dipped into a large volume of water at 20°C. The box has walls of surface area 2400 cm², thickness 2.0 mm and thermal conductivity 0.06 W m⁻¹°C⁻¹. Calculate the rate at which the ice melts in the box. Latent heat of fusion of ice = 3.4 × 10⁵ J kg⁻¹.

A pitcher with 1-mm thick porous walls contains 10 kg of water. Water comes to its outer surface and evaporates at the rate of 0.1 g s⁻¹. The surface area of the pitcher (one side) = 200 cm². The room temperature = 42°C, latent heat of vaporization = 2.27 × 10⁶ J kg⁻¹, and the thermal conductivity of the porous walls = 0.80 J s⁻¹ m⁻¹°C⁻¹. Calculate the temperature of water in the pitcher when it attains a constant value.

Water at 50°C is filled in a closed cylindrical vessel of height 10 cm and cross sectional area 10 cm². The walls of the vessel are adiabatic but the flat parts are made of 1-mm thick aluminium (K = 200 J s⁻¹ m⁻¹°C⁻¹). Assume that the outside temperature is 20°C. The density of water is 100 kg m⁻³, and the specific heat capacity of water = 4200 J k⁻¹g °C⁻¹. Estimate the time taken for the temperature of fall by 1.0 °C. Make any simplifying assumptions you need but specify them.

The ends of a metre stick are maintained at 100°C and 0°C. One end of a rod is maintained at 25°C. Where should its other end be touched on the metre stick so that there is no heat current in the rod in steady state?

Three rods of lengths 20 cm each and area of cross section 1 cm² are joined to form a triangle ABC. The conductivities of the rods are K_AB = 50 J s⁻¹ m⁻¹°C⁻¹, K_BC = 200 J s⁻¹m⁻¹°C⁻¹ and K_AC = 400 J s⁻¹ m⁻¹°C⁻¹. The junctions A, B and C are maintained at 40°C, 80°C and 80°C respectively. Find the rate of heat flowing through the rods AB, AC and BC.

A metal rod of cross sectional area 1.0 cm² is being heated at one end. At one time, the temperatures gradient is 5.0°C cm⁻¹ at cross section A and is 2.5°C cm⁻¹ at cross section B. Calculate the rate at which the temperature is increasing in the part AB of the rod. The heat capacity of the part AB = 0.40 J°C⁻¹, thermal conductivity of the material of the rod = 200 W m⁻¹°C⁻¹. Neglect any loss of heat to the atmosphere

A hole of radius r₁ is made centrally in a uniform circular disc of thickness d and radius r₂. The inner surface (a cylinder a length d and radius r₁) is maintained at a temperature θ₁ and the outer surface (a cylinder of length d and radius r₂) is maintained at a temperature θ₂ (θ₁ > θ₂). The thermal  conductivity of the material of the disc is K. Calculate the heat flowing per unit time through the disc.

A hollow tube has a length l, inner radius R₁ and outer radius R₂. The material has a thermal conductivity K. Find the heat flowing through the walls of the tube if (a) the flat ends are maintained at temperature T₁ and T₂ (T₂ > T₁) (b) the inside of the tube is maintained at temperature T₁ and the outside is maintained at T₂.

A composite slab is prepared by pasting two plates of thickness L₁ and L₂ and thermal conductivites K₁ and K₂. The slabs have equal cross-sectional area. Find the equivalent conductivity of the composite slab.