Test: Class 9 General Science NCERT Based - 3

30 Questions MCQ Test Science & Technology for UPSC CSE | Test: Class 9 General Science NCERT Based - 3

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Newton’s third law of motion explains the two forces namely ‘action’ and ‘reaction’ coming into action when the two bodies are in contact with each other. These two forces:


For every action, there is an equal and opposite reaction.
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The  size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.


In a rocket, a large volume of gases produced by the combustion of fuel is allowed to escape through its tail nozzle in the downward direction with the tremendous speed and makes the rocket move upward.

Which principle is followed in this take off of the rocket?

Solution: Law of conservation of momentum states that For two or more bodies in an isolated system acting upon each other, their total momentum remains constant unless an external force is applied.

Therefore, momentum can neither be created nor destroyed. Law of conservation of momentum is an important consequence of Newton’s third law of motion. Following are the examples of law of conservation of momentum:

1. Air filled balloons

2. System of gun and bullet

3. Motion of rockets


The seat belts are provided in the cars so that if the car stops suddenly due to an emergency braking, the persons sitting on the front seats are not thrown forward violently and saved from getting injured. Can you guess the law due to which a person falls in forward direction on the sudden stopping of the car?

  • Sir Isaac Newton published three laws in the 17th century. In this article, we are going to talk about Newton’s 1st law. This law does an introduction of motion of the object and the force acting on it.

  • In other words, it deals with the motion of an object and its relation to force. Newton’s first law states that: a body remains in the state of rest or uniform motion in a straight line unless and until an external force acts on it.

  • Putting Newton’s 1st law of motion in simple words, a body will not start moving until and unless an external force acts on it. Once it is set in motion, it will not stop or change its velocity until and unless some force acts upon it once more. The first law of motion is sometimes also known as the law of inertia.


Which of the following situations involves Newton's second law of motion?

  • Newton’s Second Law of Motion Newton’s second law of motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

  • The second law of motion gives us a method to measure the force acting on an object as a product of the mass of the object and the acceleration of the object which is the change in velocity with respect to time.


Newton’s first law of motion says that a moving body should continue to move forever, unless some external forces act on it. But a moving cycle comes to rest after some time if we stop pedaling it. Can you choose the correct reason for the stoppage of the cycle?

i. Air resistance

ii. Gravitational pull of the earth

iii. Friction of the road

iii. Heat of the environment

Choose the correct option:


Two objects of different masses falling freely near the surface of moon would:

Solution: Objects of different masses falling freely near the surface of the moon would have the same velocities at any instant because they will have same acceleration due to gravity


The school bags are generally provided with the broad strips because:

Solution: As we know that pressure is inversely proportional to area, so an increase in area means decrease in pressure.School bags are provided with broad straps to increase the surface area in contact with the shoulders and reduce pressure on the shoulders. If thin straps would be used, then surface area in contact with the shoulders would decrease which will lead to increase in pressure on shoulders.


Choose the correct unit for the relative density among the following:

  • The difference between the specific gravity and density is that at room temperature and pressure is 1gram per 1 cubic cm is the density of water this density is treated as a standard and density of any other material (usually liquids) is calculated relative to the , this is called relative density or specific gravity.

  • Hence, specific gravity is the ratio of the mass of a substance to that of a reference substance, let’s consider the density of honey is approx. 1.42 grams/cm3, so its specific gravity would be 1.42/1 = 1.42.

  • Notice that specific gravity is a ratio, therefore specific gravity does not have a unit, and hence specific gravity is a dimensionless physical quantity. The specific gravity of a substance will let us know if it will float or sink, it gives us the idea about relative mass or relative density.

  • If the specific gravity of a substance is below 1 then it will float and if it is greater than 1 it will sink. Relative density is the ratio of density of a substance to the density of a given reference material. Thus, it is a unit less quantity.


The earth and the moon are attracted to each other by gravitational force. The earth attracts the moon with a force that is:

  • Gravitational attraction is caused by the mass of an object. Since Earth is far more massive than the Moon, the gravitational force exerted on the Moon is far greater than that of the Moon on the Earth.

  • An example of the difference: while the Moon causes tides on the Earth, the Earth has the Moon locked so that the same face (minus some wobbling) is always visible from the Earth.


An apple falls from a tree because of the gravitational attraction between the earth and the apple. If F1 is the magnitude of the force exerted by the earth on the apple and F2 is the magnitude of the force exerted by the apple on the earth, then

Solution: The force of attraction F is equal to F2 , option (d)


In the SI system, the unit of P.E. is:

  • The term potential energy was introduced by the 19th-century Scottish engineer and physicist William Rankine. There are several types of potential energy, each associated with a distinct type of force.

  • It is the energy by virtue of an object’s position relative to other objects. We can define potential energy as: The energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.

  • Similarly, in the case of a spring, when it is displaced from its equilibrium position, it gains some amount of energy which we observe in the form of stress we feel in our hand upon stretching it.

  • We can define potential energy as a form of energy that results from the alteration of its position or state. Potential Energy Formula: The formula for potential energy depends on the force acting on the two objects.

  • For the gravitational force the formula is: W = m×g×h = mgh Where, m is the mass in kilograms g is the acceleration due to gravity h is the height in meters Unit: Gravitational potential energy has the same units as kinetic energy: kg m2 / s2 Note: All energy has the same units – kg m2 / s2, and is measured using the unit Joule (J).


What happens to the kinetic energy of the body if its velocity is doubled?

  • A force must be applied on a body to accelerate an object. Work must be done in order to apply a force. The body will move with an unvarying speed after the work has been done due to the energy provided by it.

  • The speed and the mass of the body are factors on which the energy transfer that makes up the kinetic energy depends. The kinetic energy of an object is the energy that it possesses due to its motion.

  • Kinetic energy definition is given as: The energy of an object because of its motion or the energy gained by an object from its state of rest to motion. Formula of Kinetic Energy: Following is the formula of kinetic energy: KE = 12mv2 Where, KE is the kinetic energy of the object m is the mass of an object v is the velocity of an object Kinetic energy is an example of scalar quantity which means that the quantity has only magnitude and no direction. Unit of Kinetic Energy: The SI unit of kinetic energy is Joule which is equal to 1 kg.m2.s-2. The CGS unit of kinetic energy is erg.


Expression for Power of an object is equal to:

Solution: Power is always dependent on work done, so if a person does work at different rates his power also differs at different times. This is where the concept of average-power comes into the picture.


In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of:

  • If you rub your hands together for several seconds, you'll notice that your hands feel warm.

  • That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction.

  • Friction is defined as: The resistance offered by the surfaces that are in contact with each other when they move over each other.

  • Friction works in the opposite direction in which the body is moving making the body slow down. Friction is useful in most of the cases. Friction is also dependent on the external factors. Factors


The value of 1 KiloWatt Hour is


According to the law of conservation of energy,

  • Energy is required for the evolution of life forms on earth. In Physics, it is defined as the capacity to do work. We know that energy exists in different forms in nature. You have learned about various forms of energy – heat, electrical, chemical, nuclear, etc. In this article, we will learn about the laws and principles that govern energy.

  • This law is known as the law of conservation of energy. What is the Law of Conservation of Energy? The law of conservation of energy states that energy can neither be created nor be destroyed. Although, it may be transformed from one form to another.


On an object the work done does not depend upon:

Solution: The amount of work done depends on the amount of the force applied and the distance object moves along with the angle between force and displacement. W = F×S×cosθ


What is the smallest unit of power?

Solution: Watt is the smallest unit of power.


Which of the following devices converts chemical energy into electrical energy?

  • Chemical energy is defined as : the energy which is stored in the bonds of chemical compounds (molecules and atoms). It is released in the chemical reaction and mostly produces heat as a by-product, known as an exothermic reaction.

  • The examples of stored chemical energy are biomass, batteries, natural gas, petroleum, and coal. Mostly, when the chemical energy is released from a substance, it is transformed into a new substance completely. For instance, when an explosion goes off, the chemical energy in it is transferred to the surroundings as thermal energy, kinetic energy, and sound energy.

Chemical Energy in Everyday Life:

• We know that plants need solar energy to produce sugar from carbon dioxide to water.

Sugar, water and carbon dioxide stay together by chemical bonds that hold the chemicals together.

• For instance, all sugars consist of oxygen, carbon and hydrogen atoms held together by chemical bonds. These atoms do not connect together automatically; rather some energy is required to make them stay together.

• Plants use solar energy to put the hydrogen, the carbon and the oxygen atoms as a whole in the form of sugar. This is a suitable example of energy transformation where energy is transformed from one form to another. Here, solar energy is transformed into chemical energy and prevents it from falling apart.


Our planet Earth receives or transfers most of its energy in the form of

  • It is actually well known that heat is simply a form of energy which transfers hotness from one point to the other. It gets transferred from one point to another by three modes of which radiation is the one.

  • The most common illustration for it is electromagnetic radiation. Light gets transferred in the form of electromagnetic radiation. Other examples are solar radiation, nuclear radiation etc Electromagnetic radiation is continuously emitted from all substances because of the molecular as well as atomic vibration accompanying the internal energy.


Match the column:


A. Microphone

B. Speaker

C. Reeds of a harmonium

D. Sails of a ship


1. Wind energy into mechanical energy

2. Mechanical energy into sound energy

3. Electrical energy into sound energy

4. Sound energy into electrical energy

Solution: Microphone − Sound energy into electrical energy. Speaker − Electrical energy into sound energy. Reeds of a harmonium − Mechanical energy into sound energy. Sails of a ship − Wind energy into mechanical energy.


Arrange the following media in ascending order of the speed of sound in them,

1. Water

2. Steel

3. Nitrogen

Solution: Self explanatory.


What is the minimum distance between two crests called?

  • Wavelength can be defined as the distance between two successive crests or troughs of a wave. It is measured in the direction of the wave.

  • Description: Wavelength is the distance from one crest to another, or from one trough to another, of a wave (which may be an electromagnetic wave, a sound wave, or any other wave).

  • Crest is the highest point of the wave whereas the trough is the lowest. Since wavelength is distance/length, it is measured in units of lengths such as metres, centimetres, millimeters, nanometres, etc.


What type of waves are Sound Waves?

  • A sound is a form of energy, just like electricity, heat or light.

  • Sound Waves are Longitudinal waves.


Which of the following is/ are not applications of Ultrasonic Waves?

A. For measuring the depth of the Sea.

B. In sterilizing of a liquid.

C. In Ultrasonography

D. In sterilizing a needle.

Solution: The speed of sound increases with the increase of temperature of the medium. The speed of sound in air increases by 0.61 m/s when the temperature is increased by 10C.


What is the unit of loudness?

Solution: The sensation of a sound perceived in an ear is measured by another term called loudness which depends on intensity of sound and sensitiveness of the ear. Unit of loudness is bel. A practical unit of loudness is decibel (dB) which is 1/10th of bel. Another unit of loudness is phon.


Which of the following statements is or are correct about longitudinal mechanical waves?

  • Sound or Audible waves are sensitive to the human ear and are generated by the vibrating bodies like tuning fork, vocal cords etc.

  • Infrasonic waves are produced by sources of bigger size such as earthquakes, volcanic eruptions, ocean waves etc. Human ear cannot detect Ultrasonic waves.


Due to which phenomena sound is heard at longer distances in nights than in day?

Solution: Due to refraction, sound is heard at longer distances in nights than in day.


Name the characteristic of the sound which distinguishes a sharp sound from a grave or dull sound?

Solution: Pitch is that characteristic of sound which distinguishes a sharp or shrill sound from a grave or dull sound. It depends upon frequency. Higher the frequency higher will be the pitch and shriller will be the sound and vice versa.


What will be the effect of temperature on speed of sound?

Solution: The speed of sound increases with the increase of temperature of the medium. The speed of sound in air increases by 0.61 m/s when the temperature is increased by 10C.
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