21.

A wide hose pipe is held horizontally by a fireman. It delivers water through a nozzle at one litre per second. On increasing the pressure. this increases to two litres per second. The firman has now to

• push forward twice as hard

• push forward four times as hard

• push backward four times as hard

• push backward twice as hard

A liquid is allowed into a tube of truncated cone shape. Identify the correct statement from the following.

• The  speed is high at the wider end and low at the narrow end

• The speed is low at the wider end and high at the narrow end.

• The speed is same at both ends in a streamline flow.

• The liquid flows with the uniform velocity in the tube.

Two soap bubbles coalesce. It is noticed that whilst joined together, the raddii of the bubbles are a and b where a>b. Then the radius of curvature of the interface between the two bubbles will be

• a-b

• a+b

• ab/(a-b)

• ab/(a+b)

The displacement of a particle along the x-axis is given by x = a sin² ωt. The motion of the particle corresponds to 

• Simple harmonic motion of frequency ω/π

• Simple harmonic motion of frequency  3ω/2π

• non-simple harmonic motion

• Simple harmonic motion of frequency ω/2π

Mercury boils at 367° C. However, mercury thermometers are made such that they can measure temperature upto 500°C. This is done by

• maintaining vacuum above mercury column in the stem of the thermometer.

• filling nitrogen gas at high pressure above the mercury column.

• filling oxygen gas at a high pressure above mercury column.

• filling nitrogen gas at a low pressure above the mercury column.

Two identical glass spheres filled with air are connected by a horizontal glass tube. The glass tube contains a pellet of mercury at its mid-point. Air in one sphere is at 0°C and the other is at 20°C. If both the vessels are heated through 10°C, then neglecting the expansions of the bulbs and the tube.

• the mercury pellet gets displaced towards the sphere at a lower temperature.

• The mercury pellet gets displaced towards the sphere at a higher temperature

• The mercury pellet does not get displaced at all.

• the temperature rise causes the pellet to expand with any displacement.

A graph between pressure P (along with the y-axis) and absolute temperature, T (along with the x-axis) for equal moles of two gases have been drawn. Given that the volume of the second gas is more than the volume of first gas. Which of the following statement is correct?

• Slope of gas 1 is less than gas 2

• Slope og gas 1 is more than gas 2

• Both have some slopes

• None of the above

A piece of blue glass heated to a high temperature and a piece of red glass at room temperature are taken inside a dimly-lit room. Then,

• The blue piece will look blue and the red piece will look red as usual.

• the red piece will look brighter red and the blue piece will look ordinary blue.

• the blue will look brighter as compared to the red piece.

• Both the pieces will look equal red.

p-V plots for two gases during the adiabatic process as shown in figure plots 1 and 2 should correspond respectively to

• He and O₂

• O₂ and He

• He and Ar

• O₂ and N₂

The temperature of source and sink of a heat engine are 127^oC and 27^oC, respectively. An inventor claims its efficiency to be 26%, then 

• It is impossible

• It is possible with high probability

• It is possible with low probability

• Data are insufficient