Chapter:2 Kinematics (9th physics new book)

Chapter: 2 Kinematics

Q1.            Is it possible that displacement is zero but not the distance? Under what condition displacement is equal to the distance?

Statement:

Displacement is zero but not the distance and displacement is equal to the distance.

Main idea:

                  Definition of displacement and distance.

Conclusion:

Yes it is possible that displacement is zero but not the distance. When an object moves in a circle and complete one round trip its displacement become zero while the distance covered is not zero and is equal to 2πr.

The displacement and distance covered is equal if and only if the body is moving in a straight line.

                                               A                 B

Q2.            Does speedometer measure a car’s speed or its velocity?

Statement:

                  Speedometer measure a car’s speed or its velocity.

Main idea:

                  Definition of speed and velocity.

Conclusion:

The speedometer of a car measures only magnitude of velocity not the direction. Therefore, we can say that speedometer of the car does not measure it velocity.

Q3.            Is it possible for an object to be accelerating and at rest at the same time? Explain with example.

Statement:

                  An object be accelerating and at rest at the same time.

Main idea:

                  Gravitational acceleration (free fall motion).

Conclusion:

Yes it possible for an object to be accelerating and at rest at the same time.

Example:

When a body is thrown upward then the velocity decreases and reaches to zero but the body is still under acceleration due to gravity (g = - 9.8 m/s²)

Q4.            Can an object have zero acceleration and non-zero velocity at the same time? Give example.

Statement:

                  An object have zero acceleration and non-zero velocity at the same time.

Main idea:

Definition of acceleration and velocity.

Conclusion:

Yes an object have zero acceleration and non-zero velocity at the same time.

Example:

Suppose a body is moving with a uniform velocity of 5m/s from point A to B. So the initial velocity of the body v_i = 5m/s at point A and final velocity is v_f = 5 m/s at point B. Now acceleration is

a =   v_f  - v_i =  5m/s  - 5m/s = 0 m/s²

            t                t

Hence acceleration a = 0 m/s² for non-zero velocity of 5 m/s.

Q5.            A person standing on the roof of a building throws a rubber ball down with a velocity of 8 m/s. What is the acceleration (magnitude and direction) of the ball?

Statement:

A person standing on the roof of a building throws a rubber ball down with a velocity of 8 m/s and acceleration of the ball.

Main idea:

                  Gravitational acceleration (free fall motion).

Conclusion:

According to famous scientist Galileo all bodies falling toward earth with a constant acceleration of g = 9.8 m/s². Now a person standing on the roof a building throws a rubber ball down with a velocity of 8 m/s. The acceleration of the ball will be g = 9.8 m/s² directed toward the earth.

Q6.            Describe a situation in which the speed of an object is constant while the velocity is not.

Statement:

                        A situation in which the speed of an object is constant while the velocity is not.

Main idea:

                  Definition of uniform speed and uniform velocity.

Conclusion:

A situation in which the speed of an object is constant while the velocity is not constant, may be that of circular motion. Suppose a body is moving with a constant speed of 5m/s in a circle. Then the speed of the body will be uniform while velocity of the body is changing at each point.

a

 

                                                                                                     V

                                                                                                                                      

Q7.            Can an object have northward velocity and a southward acceleration? Explain.

Statement:

                   An object have northward velocity and a southward acceleration.

Main idea:

            Negative acceleration (deceleration).

Conclusion:    

       Yes an object have northward velocity and a southward acceleration when a body is moving towards north and gradually its velocity decreases. Now the acceleration (deceleration) produced will be in southward direction.

                                                S                                                           N

                                                                      -a  

Q8.            As a freely falling object speeds up, what is happening to its acceleration – does it increases, decreases, or stay the same?

Statement:

                   A freely falling object speeds up and acceleration.        

Main idea:

                  Gravitational acceleration (free fall motion).

Conclusion:

                  According to famous scientist Galileo all bodies falling toward earth with a constant acceleration of g = 9.8 m/s². The acceleration will be g = 9.8 m/s² and it does not increase, decrease but stay the same.

Q9.            A ball is thrown vertically upward with an initial speed of 5m/s. What will its speed be when it returns to its starting point?

Statement:

                         A ball is thrown vertically upward with an initial speed of 5m/s and its speed when it returns to its starting point.

Main idea:

                  Gravitational acceleration (free fall motion).

Conclusion:

                  The body returns to its starting point with the same speed of 5m/s in the absence of air resistance.

9th physics chapter:1 Physical quantities and measurement

Q1. How technology shaped by physics?

Technology shaped by physics in many ways

Technology	Physics
Steam engine	Laws of thermodynamics
Nuclear reactor	Controlled nuclear fission
Radio and Television	Generation, propagation and detection of electromagnetic waves
Computers	Digital logic gates
Rocket propulsion	Newton’s laws of motion
Sonar	Reflection of ultrasonic waves
Optical fibers	Total internal reflection of light
Non-reflecting coatings	Thin film optical interference
Electron microscope	Wave nature of electrons
Photocell	Photoelectric effect

Q2.Physics and biology are considered different branches of science, how physics links with biology?

Physics has many applications in the biological sciences.

•         i.            On the microscopic level, it helps describe the properties of cell walls and cell membranes.
•       ii.            On the macroscopic level, it can explain the heat, work, and power associated with the human body.
•     iii.            Physics is involved in medical diagnostics, such as x-rays, magnetic resonance imaging (MRI), and CT scan etc.
•     iv.            Medical therapy sometimes directly involves physics; for example, cancer radiotherapy uses ionizing radiation.
•       v.            Physics can also explain sensory phenomena, how we hear sound, how the eye detects color.

Q3.Why are measurements important?

Measurement is important because:

•    i.            Measurement is an integral part of human race, without it there will be no trade, no statistics. 
•       ii.            Kids try to compare their height, size of candy, size of dolls and amount of toys they have.
•     iii.            We measure distances between different cities.
•     iv.            We measure values in different experiments.
•       v.            To buy or sell clothes and food items we measure.

Q4.Why area is called a derived quantity?

Area is the multiplication of two base physical quantities length and width. Therefore it is known as derived physical quantity.

Mathematically

Area = length x width

A = Lx W

The SI unit of area is m².

Q5.Name any four derived units and write them as their base units?

Name of any four derived units and write them as their base units are:

S.no.	Derived unit	Base unit
I.	Square meter	m2(m.m)
II.	newton	kgms-1
III.	Cubic meter	m3(m.m.m)
IV.	joule	kgm2s-2
V.	Meter per second	m/s

Q6.Why in physics we need to write in scientific notation?

In Science one often needs to work with very large or very small numbers. These can be written more easily in scientific notation or standard form. Generally

N=M x 10ⁿ

Here N=number

M=mantissa

n= exponent

Q7.What is least count? How least count for Vernier caliper and screw gauge are defined?

The minimum length that can be measured by an instrument is called least count (L.C)

Least count for Vernier calipers

The smallest digit on the main scale divided by the total numbers on the Vernier scale is called least count of Vernier calipers. Mathematically

L.C=1mm/10 = 0.1mm or 0.01cm

Least count for screw gauge

The pitch of the screw divided by the total number of divisions on the circular scale is called least count of the screw gauge. Mathematically

L.C=1mm/100 = 0.01mm or 0.001cm

Q8.How can we find the volume of a small pebble with the help of measuring cylinder?

We can find the volume of a small pebble when water is poured in measuring cylinder and noted the volume of water V1. Then put the pebble in the cylinder gently. When the pebble is completely immersed the volume of water is read again as V₂. The volume of the pebble (∆V) is found by subtracting the first reading V₁ from the second V₂.

∆V= V₂ - V₁