Chapter 8 – Thermal Properties of Matter

Which of the following substances have greater average kinetic energy of its molecules at 10^oC?

(a) Steel                      (b) copper                   (c) Water                                (d) Mercury

Ans.    Copper

Every thermometer makes use of some property of a material that varies with temperature. Name the property used in:

• • Strip thermometers
  • Mercury thermometers

Ans.    (a) In strip thermometers, colour variation is used.

            (b) Uniform thermal expansion of liquids is used in mercury thermometer.

How specific heat differs from heat capacity?

Ans.

Specific Heat	Heat capacity
·       Specific heat of a substance is the amount of heat required to raise the temperature of 1 kg mass of that substance through 1K. ·       Its unit is Jkg–1K–1	·       Heat capacity of a body is the quantity of thermal energy absorbed by it for one Kelvin (1 K) increase in its temperature. ·       Its unit is JK–1.

Give two uses of cooling effect by evaporation.

Ans.    i. Evaporation of perspiration helps to cool our body.

ii. In refrigerator evaporation of liquefied gas produces to cooling.

How evaporation differs from vaporization?

Ans.

Evaporation	Vaporization
Evaporation is the changing of a liquid into vapours (gaseous state) from the surface of the liquid without heating it.	The process in which liquid converts into gas at its boiling point is called vaporization.

Chapter 6 – Work & Energy

A crate is moved by pulling the rope attached to it. It moves 10m on a straight horizontal road by a force of 100 N. How much work will be done if

(1) The rope is parallel to the road.
Ans. As we know that W = FS cosθ.
If the rope is parallel to the road then θ = 0.
So
W = 100 x 10 x cos0
W = 100 x 10 x 1 (as cos0 = 1)
W = 1000 J

(2) The rope is making angle of 30o with road.
Ans. As we know that W = FS cosθ.
If the rope is parallel to the road then θ = 30o.
So
W = 100 x 10 x cos30o
W = 100 x 10 x 0.866 (as cos0 = 0.866)
W = 866 J

Chapter 5 – Gravitation

Does an apple attract the Earth towards it?

Ans:    Yes, Apple attracts the earth but this force is very very small so it is unable to pull the earth.  

With what force an apple weighing 1N attracts the Earth?

Ans:    Apple weighing 1N attracts the earth with a force of 1 N.

Does the weight of an apple increase, decrease or remain constant when taken to the top of a mountain.

Ans:    As we go to the mountains, value of g decreases. So weight of the apple decrease.  (As w = mg)

Chapter 4 – Turning Effect of Forces

 

A force of 150 N can loosen a nut when applied at the end of a spanner 10cm long.

F          =          150 N

L          =          10 cm =          0.1 m

So

t          =          F x L

t          =          150 x 0.1

t          =          15 Nm

What should be the length of the spanner to loosen the same nut with a 60 N force?

Ans:    As

t          =          F x L

15        =          60 x L

L          =         15 / 60

L          =          0.25 m

L          =          25 cm

How much force would be sufficient to loosen it with a 6 cm long spanner?

Ans:    As

L          =          6 cm =          0.06 m

t          =          F x L

15        =          F x 0.06 m

L          =    15 / 0.06

L          =          250 N

Can a smart child play with a fat child on the see-saw? Explain how?

Ans:    Yes, Fat child can play with smart child by adjusting the moment arm.

Two children are sitting on the see-saw, such that they can not swing. What is the net torque in this situation?

Ans:    In this case, net torque such that they can swing. In this case, net torque would be zero because clockwise torque is equal to Anticlockwise torque.

A ladder leaning at a wall as shown in figure 4.31 is in equilibrium. How?

Ans:    Ladder is in equilibrium because it satisfies second condition of equilibrium.

The weight of the ladder in figure 4.31 produces an anticlockwise torque. The wall pushes the ladder at its top end thus produces a clockwise torque. Does the ladder satisfy second condition for equilibrium?

Ans:    Yes, it satisfies second condition of equilibrium because both torques are equal in magnitude but opposite in direction.

Does the speed of a ceiling fan go on increasing all the time?

Ans:    Speed of ceiling fan does not increase all the times. At acquiring maximum speed it moves with uniform speed.  

Does the fan satisfy second condition for equilibrium when rotation with uniform speed?

Ans:    No, it does not satisfy the second condition of equilibrium. Because it neither in the state of rest nor moving with uniform velocity.

Chapter 3 – Dynamics

Stretch out your palm and hold a book on it.

• How much force you need to prevent the book from falling?

Ans.    Force equal to the weight of the book is needed to prevent the book from falling.

• Which is action?

Ans.    Weight of the book is action in this case.

• Is there any reaction? If yes, then what is its direction?

Ans.    Yes there is a reaction offered by hand. The direction of reaction is opposite to the weight.

• Which shoe offer less friction?

Ans.    Shoe with flat sole will offer less friction

• Which shoe is better for walking on dry track?

Ans.    On dry track, shoe with flat sole is batter for walking.

• Which shoe is better for jogging?

Ans.    Shoe which has not flat sole is batter for jogging.

• Which sole will wear out early?

Ans.    Shoe with flat sole will wear out early.

• Why is it easy to roll a cylindrical eraser on a paper sheet than to slide it?

Ans.    It is easy to roll a cylindrical eraser on a paper sheet than to slide it because rolling friction is less than sliding friction.

• Do we roll or slide the eraser to remove the pencil work from our notebook?

Ans.    We slide the eraser to remove the pencil work from our notebook because we need more friction to remove the work and sliding friction is greater than rolling friction.

• In which case do you need smaller force and why?

            (i) rolling                   (ii) sliding

Ans.    Rolling: Incase of rolling friction we need smaller force because there is contact with earth on only a single point.

            Sliding: Incase of sliding friction we need greater force because all the body is in contact with the earth.

• In which case it is easy for the tyre to roll over?

            (i) rough ground       (ii) smooth ground

Ans.    Rough ground: Incase of rough ground it is difficult for the tyre to roll over because rough surface offer more friction.

            Smooth ground: Incase of smooth ground it is easier for the tyre to roll over because smooth surface offer less friction.

Chapter 2 – Kinematics

When a body is said to be at rest?

Ans:    When a body does not change its position with respect to its surroundings. Then it is said to be in the state of rest.

 

Give an example of a body that is at rest and is in motion at the same time.

Ans:    If a person is sitting in a moving car, he will be in the state of rest with respect to the other person sitting in the car and he will be in the state of motion with respect to the person standing on the road side at the same time.

 

Mention the type of motion in each of the following.

• A ball moving vertically upward.

Ans:    Linear motion (Translatory motion)

• A child moving down a slide.

Ans:    Linear motion (Translatory motion)

• Movement of a player in a football ground.

Ans:    Random motion (Translatory motion)

• The flight of a butterfly.

Ans:    Random motion (Translatory motion)

• An athlete running in a circular track.

Ans:    Circular motion (Translatory motion)

• The motion of a wheel.

Ans:    Rotatory motion

• The motion of a cradle.

Ans:    Vibratory motion

Chapter 1 – Physical Quantities & Measurement

Why do we study physics?

Ans.    The rapid progress in science during the recent years has become possible due to the discoveries and inventions in the field of Physics. Most of the technologies of our modern society throughout the world are related to Physics. In order to get knowledge about these techniques, technologies, scientific principles and to play a vital role in new discoveries and inventions we study physics.

 

Name any five branches of Physics.

Ans.    (i) Mechanics (ii) Heat          (iii) Sound      (iv) Light (Optics)      (v) Atomic Physics

 

How can you differentiate between base and derived quantities? (GRW 2014, 2015)

Base Quantities	Derived Quantities
The quantities on the basis of which other quantities are expressed are known as base quantities. Example length, time, mass	All the quantities, which can be described in terms of base quantities, are known as derived quantities. Example Force, area, volume, density etc

 

Identify the following as base or derived quantity:

Density, force, mass, speed, time, length, temperature and volume.

Base units	Derived Units
Mass, time, length, temperature	Density, force, speed, volume

 

Name five prefixes most commonly used.

• • Kilo (k) = 10³
  • Mega (M) = 10⁶
  • Micro (m) = 10^–6
  • Milli (m) = 10^-3
  • Nano (n) = 10^-9

 

The Sun is one hundred and fifty million kilometers away from the Earth. Write this

(a) As an ordinary whole number.

150, 000, 000 km

(b) In scientific notation

1.5 x 10⁸ km

 

Write the numbers given below in scientific notation

(a) 3000000000 ms^-1

3.0 x 10⁹ ms^-1

(b) 6400000 m

6.4 x 10⁶ m

(c) 0.0000000016 g

1.6 x 10^-9 g

(d) 0.0000548 s

5.48 x 10^-5

 

What is the least count of the Vernier Callipers?

Ans.    The difference between one small division on main scale and one vernier scale division is       0.1 mm. It is called least count of vernier callipers.

 

How many divisions are there on Vernier scale of vernier callipers?

Ans.    There are 10 division on Vernier scale of the vernier calipers.

 

Why do we use zero correction?

Ans.    We use zero correction to take a correct measurement free of error.

 

What is the least count of a screw gauge?

Ans.    The minimum measurement which can be taken using a screw gauge is known as its least       count. The least count of screw gauge is 0.01 mm or 0.001 cm.

 

What is the pitch of your laboratory screw gauge?

The pitch of laboratory screw gauge is 1mm.

 

Which one of the two instruments is more precise and why?

(a) Vernier calipers

(b) Screw Gauge

Screw gauge is more precise than vernier callipers because it can measure accurately up to one hundredth part of a millimeter while vernier callipers can only measure accurately up to one tenth part of a millimeter.

 

What is the function of balancing screws in physical balance?

The function of balancing screws is to bring the pointer at zero position on raising the beam.

 

On what pan we place the object and why?

We place the object on left pan and standard masses on the right pan just for the convenience of user.