# Class 9 Physics Properties of matter vii. According to Hookes law(a) stress x strain = constant(b) stress / strain = constant(c) strain / stress = constant(d) stress = strain

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##### vii. According to Hookes law(a) stress x strain = constant(b) stress / strain = constant(c) strain / stress = constant(d) stress = strain

viii. Which of the following affects evaporation?(a) temperature(b) surface area of the liquid(c) wind(d) all of the above

7.12 Why does the atmospheric pressure vary with height?

7.11 What makes a sucker pressed on a smooth wall sticks to it?

9. Evaporation can occur ata) freezing pointb) melting pointc) boiling pointd) all temperatures

iii. Mercury is used as thermometric material because it has(a) uniform thermal expansion(b) low freezing point(c) small heat capacity(d) all the above properties

EXAMPLE 8.2Change 300 \mathrm{~K} on Kelvin scale into Celsius scale of temperature.

EXAMPLE 8.1What will be the temperature on Kelvin scale of temperature when it is 20^{\circ} \mathrm{C} on Celsius scale?

EXAMPLE 7.1The mass of 200 \mathrm{~cm}^{3} of stone is 500 \mathrm{~g} . Find its density.

EXAMPLE 7.2In a hydraulic press a force of 100 \mathrm{~N} is applied on the piston of a pump of cross-sectional area 0.01 \mathrm{~m}^{2} . Find the force that compresses a cotton bale placed on larger piston of cross-sectional area 1 \mathrm{~m}^{2} .

c) In which state of matter the molecules are most closely packed?

11. Linear thermal expansion of a solid depends upona) increase in temperatureb) originallengthc) properties of materiald) all of these

EXAMPLE 7.6A barge 40 metre long and 8 metre broad whose sides are vertical floats partially loaded in water. If 125000 \mathrm{~N} of cargo is added how many metres will it sink?

EXAMPLE 8.5 A container has 2.5 litres of water at 20^{\circ} \mathrm{C} . How much heat is required to boil the water?

9. Air at atmospheric pressure of 760 \mathrm{~mm} of \mathrm{Hg} is trapped inside a container available with a moveable piston. When the piston is pulled out slowly so that the volume is increased from 100 \mathrm{dm}^{3} to 150 \mathrm{dm}^{3} the temperature remaining constant. What will be the pressure of the air becomes?

7.1 A wooden block measuring 40 \mathrm{~cm} \times 10 \mathrm{~cm} \times 5 \mathrm{~cm} has a mass 850 g. Find the density of wood. \left(425 \mathrm{kgm}^{3}\right)

ii. Which of the substances is the lightest one?(a) copper(b) mercury(c) aluminum (d) lead

c) Which state of matter is highly incompressible?

10. Rate of evaporation of a liquid can be increased bya) increasing humidityb) decreasing temperaturec) increasing its boiling pointd) decreasing atmospheric pressure

EXAMPLE 8.4 Convert 100^{\circ} \mathrm{F} into the temperature on Celsius scale.

Worked Example 1A cylinder contains 60 \mathrm{~cm}^{3} of air at a pressure of 140 \mathrm{kPa} . What will its volume be if the pressure on it is increased to 420 \mathrm{kPa} ?

iii. SI unit of pressure is pascal which is equal to:(a) 10^{4} \mathrm{Nm}^{-2} (b) 1 \mathrm{Nm}^{-2} (C) 10^{2} \mathrm{Nm}^{-2} (d) 10^{3} \mathrm{Nm}^{-2}

7.1 Encircle the correct answer from the given choices:i. In which of the following state molecules do not leave their position?(a) solid(b) liquid(c) gas(d) plasma

EXAMPLE 7.7 A steel wire 1 \mathrm{~m} long and cross-sectional area 5 \times 10^{-5} \mathrm{~m}^{2} is stretched through 1 \mathrm{~mm} by a force of 10000 N. Find the Youngs modulus of the wire.

7.10 Why water is not suitable to be used in a barometer?

7. A gas in a container of fixed volume is heated. What happens to the molecules of the gas?a) They collide less frequently.b) They expand.c) They move faster.d) They move further apart.