1. Ball bearings are used in bicycles, cars, etc., because

(a) the actual area of contact between the wheel and axle is increased

(b) the effective area of contact between the wheel and axle is increased

(c) the effective area of contact between the wheel and axle is reduced

(d) None of the above statements is correct

(c) Ball bearings are used to reduce friction and friction is directly proportional to effective surface area. So if effective surface area is reduced then friction will also reduce.

2. The clouds float in the atmosphere because of their low :

(a) temperature

(b) velocity

(c) pressure

(d) density

(d) Because of density. The density of the clouds is less than that of the air.

3. Low temperatures (cryogenics) find application in :

(a) space travel, surgery and magnetic levitation

(b) surgery, magnetic levitation and telemetry

(c) space travel, surgery and telemetry

(d) space travel, magnetic levitation and telemetry

(a) In physics, cryogenics is the study of the production of very low temperature (below –150 °C,

– 238 °F or 123 K) and the behavior of materials at those temperatures. Application of cryogenics are in

MRI. MRI is a method of imaging objects that uses a strong magnetic field to detect the relaxation of protons that have been perturbed by a radio-frequency pulse. This magnetic field is generated by electromagnets, and high field strengths can be achieved by using superconducting magnets. Traditionally, liquid helium is used to cool the coils because it has a boiling point of around 4 K at ambient pressure. Cryogenic liquids are also used in the space program. For example, cryogens are used to propel rockets into space. A tank of liquid hydrogen provides the fuel to be burned and a second tank of liquid oxygen is provided for combustion. Cryogenic processes are also used to supply "banks" storing eye corneas, blood, and sperm for future surgical procedures. In 1961 American surgeon Irving S. Cooper introduced a freezing technique called cryosurgery. Cryosurgery is relatively bloodless because the low temperatures used constrict the blood vessels, stemming the loss of blood.

4. Assertion (A) : A piece of copper and a piece of glass are heated to the same temperature. When touched, thereafter, the copper piece appears hotter than the glass piece.

Reason (R) : The density of copper is more than that of glass.

Codes:

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

(b) Both statement 1 and statement 2 are correct. On heating up to same temperature copper piece is found hotter than in comparison to glass piece because copper being a metal is a good conductor of heat and electricity while glass on the other hand is a poor conductor of heat. The density of copper is 8.92 gm/cm3 and of glass is 2.6 gm/cm3 .

5. Assertion (A) : The boiling point of water decreases as the altitude increases.

Reason (R) : The atmospheric pressure increases with altitude.

Codes :

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

(c) The boiling point of an element or a substance is the temperature at which the vapour pressure of the liquid equals the environmental pressure surrounding the liquid. As altitude increases, atmospheric pressure decreases, so boiling point decreases, so the liquid would boil at a lower temperature.