9th Physics Full book Short questions
9th Physics Full book Short questions.
Chapter 1
Q 1.1 Can a non-physical quantity be measured ? If yes, then how ?
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No. With the help of using tools and instruments, we cannot measure a non-physical quantity because it does not have a defined physical unit. Love, beauty, honesty and trust are non-physical quantities.
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Q 1.2 What is measurement ? Name its two parts
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Measurement is a process of comparison of an unknown quantity with a standard quantity (unit).
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Measurement consists of two parts, a number (magnitude or numerical value) and a unit. In 5 meters, 5 is magnitude and meter is unit.
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Q 1.3 Why do we need a standard unit for measurement ?
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Standard unit for measurement can be for efficient working and growth of trade, business and share scientific information.
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Q 1.4 Write the name of 3 base quantities and 3 derived quantities.
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Base quantities are length, mass and time.
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Derived quantities are area, volume and speed.
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Q 1.6 Write the name and symbols of all SI base units.
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| Name of Unit | Symbol of Unit |
|---|---|
| Meter | m |
| Kilogram | kg |
| Second | s |
| Kelvin | K |
| Ampere | A |
| Candela | cd |
| Mole | mol |
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Q 1.7 Why prefix is used ? Name three sub-multiples and three multiple prefixes with their symbols.
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We use prefix to make unit simple and easy. Three sub-multiples are deci, centi and milli denoted by d, c and m respectively.
Three multiples are kilo, mega and giga denoted by k, M and G respectively.
Chapter 2
2.1 Define scalar and vector quantities.
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Scalar
A scalar is that physical quantity which needs magnitude only to describe it completely.
Vector
A vector is that physical quantity which needs magnitude as well as direction to describe it completely.
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2.2 Give 5 examples each for scalar and vector quantities.
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Examples of scalars are distance, speed, mass, time, temperature, and energy.
Examples of vector are displacement, velocity, acceleration, force, torque and momentum.
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2.3 State head-to-tail rule for addition of vector.
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To add vectors, we apply a rule called head-to-tail rule.
Definition of head to tail rule.
To add vectors, we draw their representative lines such that the head of one line coincides with the tail of the other. The resultant vector is given by a single vector which is directed from the tail of the first vector to the head of the last vector.
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2.4 What are distance-time graph and speed-time graph.
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Distance-time graph shows the relation between distance S and time t taken by a body.
We take time t along x-axis and distance s along y-axis
Gradient (slope) of distance-time graph gives us speed.
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Speed-time graph shows the relation between speed V and time t taken by a body.
We take time t along x-axis and speed v along y-axis
Gradient (slope) of speed-time graph gives us acceleration.
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2.5 Falling objects near the Earth have the same constant acceleration. Does this imply that a heavier object will fall faster than a lighter object?
No, heavier object will not fall faster than a lighter object in the absence of air resistance.
Weight of any body will not affect the rate of free fall.
$$g\;=\;9.8\;m\;s^{-2}\;\approx\;10\;m\;s^{-2}$$
Chapter 3
Q1 What kind of changes in motion may be produced by a force ?
Force can change the speed, direction, shape, size and state of an object.
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Q2 Give 5 examples of contact forces.
A force that is exerted by one object on the other at the point of contact is called contact force.
Examples of contact forces are friction, thrust, air resistance, drag force, normal force, tension force and elastic force.
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Q3 An object moves with a constant velocity in free space. How long will the object continue to move with this velocity ?
Due to Newton’s first law of motion the object will move forever unless the object experiences an external force.
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Q4 Define impulse of force ?
Impulse is the total change in momentum of an object.
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Q5 Why has not Newton’s first law been proved on the Earth ?
There is no proof of Newton’s first law on Earth. Because according to science, Earth is continuously rotating about the sun and spinning about its own axis.
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Q6 When sitting in a car which suddenly accelerates from rest, you are pushed back into the seat, why ?
It happens due to inertia. Body is initially at rest. When car suddenly accelerates, body resists due to inertia but seat pushes you forward. As a result, seat pushes you back.
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Q9 Define terminal velocity of an object.
Terminal velocity is the constant maximum velocity of a freely falling object when the force of gravity is balanced by the air resistance and no further acceleration occurs.
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Chapter 4
4.1 Define like and unlike parallel forces.
We call parallel forces acting in same direction ” like parallel forces ” and those acting in opposite direction ” unlike parallel forces’.
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4.2 What are rectangular components of a vector and their values?
We resolve a force into two components that are perpendicular to each other. We call these components as perpendicular or rectangular components of the force.
$$Horizontol\;component\\is\;represented\;by\;F_x$$ $$F_x=F\;Cos\theta$$
$$Vertical\;component\\is\;represented\;by\;F_y$$ $$F_y=F\;Sin\theta$$
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4.3 What is the line of action of a force?
The line along which the force acts is called the line of action of the force.
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4.4 Define moment of a force. Prove that
$$\tau\;=\;rF\;Sin\theta$$ where Ɵ is angle between r and F.
Moment of the force or torque is defined as the product of the force and the moment arm.
Let a force F is applied on an object at point P which is at a distance r from the origin.
$$Angle\;between\;r\;and\;F\;is\;\theta.\\Horizontal\;and\;vertical\\components\;of\;force\;F\\are\;F\;Cos\theta\;and\;F\;Sin\theta\\respectively.$$
There will be rotation only due to vertical component of force and no rotation due to horizontal component of the force because the line of action of horizontal component of force will pass through the origin.
We call perpendicular distance from the line of action of force to the origin the moment arm, denoted by r.
$$Torque=Moment\;arm\times force\\\tau\;=\;r\;F_y\\\tau\;=\;r\;F\;S\mathrm{in}\theta\;\\$$
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4.7 Give an example of the body which is moving yet in equilibrium.
A car which is moving on a straight road at constant speed is in dynamic equilibrium.
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Chapter 5
5.1 what is the work done on an object that remains at rest when a force is applied on it?
Work done is the product of force and displacement in the direction of the force. Because there is no movement, so there is no work
W = Fd = F(o) = 0 J
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5.2 A slow moving car may have more kinetic energy than a fast moving motorcycle .How is it possible ?
Due to heavy mass of car, its energy will be greater than the energy of motorcycle.
$$K.E\;=\;\frac12mv^2$$
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5.4 A women runs up a flight of stairs . The gain in her gravitational potential energy is 4500J. If she runs up the same stairs with twice the speed, what will be her gain in potential energy ?
Running faster means she does the same work in less time. Hence her power increases but not the potential energy because potential energy depends on mass, gravitational acceleration and height not the time. Her potential energy be again 4500 J.
P.E = mgh
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5.5 Define work and its SI units .
Work is defined as the product of magnitude of force and the distance covered in the direction of the force. SI unit of work is Joule. it is denoted by J. One joule work is done when a force of 1 Newton acting on a body moves it through a distance of 1 meter in its own direction.
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5.7 Find an expression for the kinetic energy of a moving body?
$$K.E\;=\;\frac12mv^2$$
Where m is mass of the body and v is the speed of the body.
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5.8 Define efficiency of a working system . Why a system cannot have 100% efficiency?
Efficiency of a working system is the ratio of useful output energy and the total input energy.
Energy output is always less then the input energy. We cannot convert all the input energy into required output, hence we can obtain 100% efficiency.
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5.9 What is power? Define the unit used for it.
Power is defined as the time rate of doing work. Power = Work/Time
Watt is SI unit of Power. It is denoted by W. Watt is defined as the work done at the rate of 1 Joule per second.
1KW = 1000 watts
One Horse Power ( hp ) = 746 watts
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Chapter 6
6.1 Why heavy animal like an elephant have a large area of the foot?
Animals like elephant have large area of foot to reduce the pressure they exert on the ground. Pressure is equal to force per unit area.
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6.3 Why is it painful to walk bare footed on pebbles?
It is painful to walk bare footed on pebbles due to pebbles small surface area. Force ( weight of the body ) creates high pressure on small pebbles which causes pain at the point where pebbles contact with the feet.
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6.4 State pascal ‘s law? Give an application of pascal’s law?
Pascal’s law states that when pressure is applied at one point in an enclosed fluid, it is transmitted equally to all parts of fluid without loss.
Applications of Pascal’s law
i):- Air pressure spreads equally inside the balloon to make it expand.
ii):- Brust if tyre and hydraulic lift are also examples of Pascal’s law.
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6.5 State what do you mean by elasticity of a solid?
A object is said to be elastic, if after removal of the deforming force, it restores to its original size and shape. This property of material is known as elasticity.
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6.7 Distinguish between force and pressure?
Force is an agency which changes or tries to change the state of an object. Pressure is the force per unit area.
Force is total push or pull while pressure tells us how concentrated the force is over the given area.
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6.8 What is the relationship between liquid pressure and the depth of the liquid?
$$P\;=\;\rho\;g\;h\;\\where\;P\;is\;pressure\;at\;depth\\\rho\;is\;density\;of\;the\;liquid\\g\;is\;gravitional\;acceleration\\and\;h\;is\;depth\;of\;the\;liquid$$
Liquid pressure increases with the depth. As depth h increases, more liquid is above at that point, so more weight is pressing down. This causes greater pressure on objects at lower depths.
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6.10 State the basic principal used in the hydraulic brake system of the automobiles?
Basic principal used in the hydraulic brake system of the automobiles is Pascal’s law. When pressure is applied to a liquid in a closed system, it is transmitted equally in all directions.
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Chapter 7
Q4 What is the effect of raising the temperature of a liquid?
Due to raise in temperature of a liquid molecular motion increases, viscosity decreases, rate of evaporation increases and expansion occurs.
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Q5 What is meant by temperature of a body? Define heat as’ energy in transit.
Temperature of a body is the measurement of the average kinetic energy of the molecules of the that body.
Heat is energy in transit from one body to another because of temperature difference.
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Q7 State the main scales used for the measurement of temperature.
We use three main scales for the measurement of temperature. Celsius scale, Fahrenheit scale and Kelvin scale. Other name of Celsius scale is Centigrade scale.
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Q8 What is meant by sensitivity of a thermometer?
Sensitivity of a thermometer means how clearly and quickly a thermometer responds to a small temperature change.
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Q12 Distinguish between the heat and internal energy.
Heat is energy in transit due to temperature difference. It flows from hot object to clod object. We will denote heat by Q.
Internal energy is the total energy of molecules inside a body. It does not flow. We will denote internal energy by U or E.
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Q13 When you touch a cold surface, does cold travel from the surface to your hand or does energy travel from your hand to cold surface?
No, cold does not travel from cold surface. Energy flows from warm hand to cold surface, making the hand feel cold.
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Chapter 8
8.1 What are temporary and permanent magnets?
Temporary magnets are materials that act like a magnet only when they are placed in a strong magnetic field. Its example is soft iron.
Permanent magnets are materials that keep their magnetism for a long time even when the external magnetic field is removed. Its example is bar magnet.
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8.2 Define magnetic field of a magnet.
A magnetic field is the region around a magnet where another magnetic object experiences a force on it.
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8.3 What are magnetic lines of force?
Magnetic lines of force are imaginary lines. We use magnetic field lines to show the direction and strength of a magnetic field. These lines always show from the north pole to the south pole out side the magnet.
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8.4 Name some uses of permanent magnets and electromagnets.
People use permanent magnets in electric motors, electric generators and moving coil loudspeakers. People use electromagnets in electric bells, circuit breakers, and telephone receivers.
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Chapter 9
9.1 State in your own words, what is science? Write its two main groups.
Science is a collective knowledge about the natural phenomena, process and events occurring around us. There are two main groups of science, the biological sciences and the physical sciences.
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9.2 What is Physics all about? Name some of its branches.
Physics is a branch of science which deals with the matter, energy and their mutual relationship. Some branches of Physics are Mechanics, Heat and thermodynamics, Acoustics, Optics, Electromagnetism, Quantum Mechanics, Relativistic Mechanics, Nuclear Physics, Particle Physics and Astronomy.
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9.4 List the main steps of scientific method.
Main steps of scientific method are observation, hypothesis, experiment, theory, prediction, falsifiability and law.
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9.5 What is a hypothesis? Give an example.
On the basis of data collected through observation or experimentation, we can develop a hypothesis. Lets check the example of hypothesis. Shadow of opaque objects are formed when they come in path of light because light travels in straight line.
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9.6 Distinguish between a theory and law of physics.
A law tells what happens and a theory explains why it happens.
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