Coal reserves are said to be enough
Question: Coal reserves are said to be enough to last for another hundred years. Do you think we need to worry in such case? Why or why not? Solution: Yes, the known resources of coal will last only for about 100 years. Once the present stock of coal present in the earth gets exhausted, no new supplies of these fossil fuels will be available to us in the near future because it take millions of years to convert the dead organisms into fossil fuels in nature. So, coal should be used with care and ...
Read More →The volume V and depth x of water in a vessel
Question: The volume $V$ and depth $x$ of water in a vessel are connected by the relation $V=5 x-\frac{x^{2}}{6}$ and the volume of water is increasing the rate of $5 \mathrm{~cm}^{3} / \mathrm{sec}$, when $x=2 \mathrm{~cm}$. The rate of which the depth of water is increasing is equal to__________________ Solution: It is given that, $\frac{d V}{d t}=5 \mathrm{~cm}^{3} / \mathrm{sec}$ The volume $V$ and depth $x$ of water in a vessel are connected by the relation $V=5 x-\frac{x^{2}}{6}$. $V=5 x-\...
Read More →Write some important uses
Question: Write some important uses of the various constituents of petroleum. Solution: (i) Petroleum gas in liquid form (LPG) is used as fuel in homes and industries. (ii) Petrol is used as fuel for automobiles and aviation. (iii) Kerosene is used as fuel for stoves, lamps and jet aircrafts. (iv) Diesel is used as fuel for heavy motor vehicles, electric generators. (v) Lubricating oil is used for lubrication. (vi) Paraffin wax is used in ointments, candles, vaseline, etc, (vii) Bitumen is used ...
Read More →Why petrol is exhaustible natural resource
Question: Why petrol is exhaustible natural resource whereas sunlight is not? Explain. Solution: The natural resources which are present in a limited quantity in nature and can be exhausted (used up) by human activities are called exhaustible natural resources, e.g. coal, petroleum, natural gas, minerals, forests, wildlife, etc. It requires millions of years for the conversion of the dead organisms into petroleum from which petrol is separated. So, once the present stock of it gets exhausted, no...
Read More →Imagine that all the exhaustible natural
Question: Imagine that all the exhaustible natural resources are exhausted by human activities. Do you think survival of living beings would be possible? If yes, why? If not, why not? Solution: If all the exhaustible natural resources are exhausted by human activities, then the survival of living beings would not be possible. Actually, fossil fuels are the most important source of energy for us today. They are concentrated source of energy and give off heat and light on burning.The heat can be u...
Read More →While driving what are the tips
Question: While driving what are the tips we must follow to save petrol/diesel/natural gas? Solution: The following tips we must follow to save petrol/diesel/natural gas as below: (i) Ensure correct air pressure in the tyres. (ii) Ensure regular maintenance of the vehicle. (iii) Driye at a constant and moderate speed as far as possible. (iv) Switch off the engine at traffic lights or at a place where you have to wait....
Read More →We read in newspapers that burning
Question: We read in newspapers that burning of fuels is a major cause of global warming. Explain why? Solution: Burning of fuels is a major cause of global warming because they produce a lot of greenhouse gas carbon dioxide on burning. The earths atmosphere allows most of the sunlight that falls on it to pass through and heat the surface. But greenhouse gases such as carbon dioxide, methane, water vapours | trap the heat radiated from earth. This leads to an increase in earths temperature. This...
Read More →We say fossil fuels will last
Question: We say fossil fuels will last only for a few hundred years. Comment. Solution: Fossil fuels will last only for a few hundred years because they are exhaustible natural resources. If consumed at a rate faster than the rate at which these are formed in nature, they will get exhausted very soon. Once the present stock of these gets exhausted, no new supplies of these fossil fuels will be available to us in the near future because it required millions of years for the conversion of dead or...
Read More →The distance s described by a particle in t seconds is given by
Question: The distance $s$ described by a particle in $\mathrm{t}$ seconds is given by $s=a e^{t}+\frac{b}{e^{t}}$. Then the acceleration of the particle at time $t$ is equal to__________________ Solution: It is given that, the distance s described by a particle in $t$ seconds is given by $s=a e^{t}+\frac{b}{e^{t}}$. The acceleration of the particle at time $t$ is given by $\frac{d^{2} s}{d t^{2}}$. $s=a e^{t}+\frac{b}{e^{t}}$ Differentiating both sides with respect to $t$, we get $\frac{d s}{d ...
Read More →Name the products obtained and
Question: Name the products obtained and their uses when coal is processed in industry. Solution: When coal is strongly heated in the- absence of air in closed retorts, various useful products are obtained. These are coke, coal tar and coal gas.Uses of coke It is used in the manufacture of steel and in the extraction of many metals. It acts as a fuel and it is a better fuel than coal.Uses of coal tar The various compounds obtained from coal tar are used as starting materials for manufacturing a ...
Read More →The distance s described by a particle in t seconds is given by
Question: The distance $s$ described by a particle in $\mathrm{t}$ seconds is given by $s=a e^{t}+\frac{b}{e^{t}}$. Then the acceleration of the particle at time $t$ is equal to__________________ Solution: It is given that, the distance s described by a particle in $t$ seconds is given by $s=a e^{t}+\frac{b}{e^{t}}$. The acceleration of the particle at time $t$ is given by $\frac{d^{2} s}{d t^{2}}$. $s=a e^{t}+\frac{b}{e^{t}}$ Differentiating both sides with respect to $t$, we get $\frac{d s}{d ...
Read More →Fill in the blanks and complete the story.
Question: Fill in the blanks and complete the story.About 300 million years ago, the earth had dense in low lying wetland areas. Due to natural processes like.. these forests got buried under the. As more.. deposited over them, they were compressed. The. also rose as they sank deeper and deeper.Under high ..and high , dead plants got slowly converted into coal. Solution: forests, floods, soil, soil, temperature, pressure, temperature....
Read More →Find the sum of the series:
Question: Find the sum of the series: $\left(2^{2}+4^{2}+6^{2}+8^{2}+\ldots\right.$ to $n$ terms $)$ Solution: In the given question we need to find the sum of the series. For that, first, we need to find the $n^{\text {th }}$ term of the series so that we can use summation of the series with standard identities and get the required sum. The series given is $\ldots 2^{2}+4^{2}+6^{2}+8^{2}+\ldots$ to $n$ terms. The series can be written as, $\left[(2 \times 1)^{2},(2 \times 2)^{2}\right.$, $\left...
Read More →Write the characteristics
Question: Write the characteristics and some important uses of coal. Solution: Characteristics of coal are as follows: (i) It is a hard, black combustible fuel. (ii) It is a fossil fuel. (iii) It mainly contains carbon. (iv) When heated in air, it burns and produces mainly carbon dioxide gas. (v) It is a source of energy. Some important uses of coal are as follows: (i) It is used as a fuel in homes and industry and at thermal power plants for generating electricity. (ii) It is used to make coal ...
Read More →Write two important uses of coke.
Question: Write two important uses of coke. Solution: (i) Coke is mainly used as a reducing agent in the extraction of metals (like iron, zinc, etc). (ii) It is used in the manufacture of steel....
Read More →Some natural resources are given below.
Question: Some natural resources are given below. Classify them into the exhaustible and inexhaustible natural resources. Air, coal, natural gas, sunlight, petroleum, minerals, forests, oxygen Solution: Exhaustible natural resources are : Coal, natural gas, petroleum, minerals, forests. Inexhaustible natural resources are : Air, sunlight, oxygen....
Read More →Sunlight and air are inexhaustible
Question: Sunlight and air are inexhaustible natural resources. Comment. Solution: These resources are present in an unlimited quantity in nature and are not likely to be exhausted by human activities. There is a never ending supply of these resources in nature. These resources can be used again and again. They last forever....
Read More →Gas is being pumped into a spherical balloon
Question: Gas is being pumped into a spherical balloon at the rate of $30 \mathrm{~cm}^{3} / \mathrm{min}$. The rate at which the radius increases when it reaches the value $15 \mathrm{~cm}$, is____________________ Solution: Letrbe the radius andVbe the volume of the balloon at timet. It is given that, $\frac{d V}{d t}=30 \mathrm{~cm}^{3} / \mathrm{min}$ Now, Volume of the spherical balloon, $V=\frac{4}{3} \pi r^{3}$ $V=\frac{4}{3} \pi r^{3}$ Differentiating both sides with respect to $t$, we ge...
Read More →Gas is being pumped into a spherical balloon
Question: Gas is being pumped into a spherical balloon at the rate of $30 \mathrm{~cm}^{3} / \mathrm{min}$. The rate at which the radius increases when it reaches the value $15 \mathrm{~cm}$, is____________________ Solution: Letrbe the radius andVbe the volume of the balloon at timet. It is given that, $\frac{d V}{d t}=30 \mathrm{~cm}^{3} / \mathrm{min}$ Now, Volume of the spherical balloon, $V=\frac{4}{3} \pi r^{3}$ $V=\frac{4}{3} \pi r^{3}$ Differentiating both sides with respect to $t$, we ge...
Read More →Write True/False against the following statements.
Question: Write True/False against the following statements. (i) Oxygen in air is an exhaustible natural resource. (ii) Resources which are present in unlimited quantity in nature are called exhaustible natural resources. (iii) Wildlife is an exhaustible natural resource. (iv) Under high temperature and pressure, dead plants get slowly converted to coal. (v) CNG is less polluting fuel than petrol and diesel. . Solution: (i) False, oxygen in air is an inexhaustible natural resource because oxygen...
Read More →Fill in the blanks.
Question: Fill in the blanks. (a) The slow protess of conversion of dead vegetation into coal is called (b) Coal and petroleum are formed from the dead remains of organisms and are known as (c) The black thick liquid with smell is known as coal tar. (d) During the processing of coal to get coke, coal tar and are also obtained. (e) The process of separating the various constituents of petroleum is known as (f) Excessive burning of fossil fuels is a major cause of Solution: (a) carbonisation (b) f...
Read More →The underlined words in the following
Question: The underlined words in the following sentences have been jumbled up. Write them in their correct form. (a) Loca is obtained from mines. (b) Umpetlore is a fossil fuel. (c) Renrfvie is a place where various fractions of petroleum are separated. (d) Keen rose is a fuel used in jet crafts. (e) Nutsoilh is an example of inexhaustible natural resources. Solution: (a) Coal (b) Petroleum (c) Refinery (d) Kerosene (e) Sunlight ....
Read More →Fill in the blanks.
Question: Fill in the blanks. (a) Coal is one of the.used to cook food. (b) When heated in air, coal burns and produces mainly .gas. (c) Coal tar is a black, thick.with an .smell. (d) Petroleum,..and.. are fossil fuels. (e) Forests and coal are .. natural resources. Solution: (a) fuels (b) carbon dioxide (c) liquid, unpleasant (d) coal, natural gas (e) exhaustible...
Read More →Fill in the blanks.
Question: Fill in the blanks. (a) Coal is one of the.used to cook food. (b) When heated in air, coal burns and produces mainly .gas. (c) Coal tar is a black, thick.with an .smell. (d) Petroleum,..and.. are fossil fuels. (e) Forests and coal are .. natural resources. Solution: (a) fuels (b) carbon dioxide (c) liquid, unpleasant (d) coal, natural gas (e) exhaustible...
Read More →Find the sum of the series whose nth term is given by:
Question: Find the sum of the series whose nth term is given by: $\left(n^{3}-3^{n}\right)$ Solution: It is given in the question that the nth term of the series, $a_{n}=n^{3}-3^{n}$ Now, we need to find the sum of this series, $S_{n}$. $\mathrm{S}_{\mathrm{n}}=\sum_{\mathrm{n}=1}^{\mathrm{n}} \mathrm{a}_{\mathrm{n}}$ $\mathrm{S}_{\mathrm{n}}=\sum_{\mathrm{n}=1}^{\mathrm{n}}\left(\mathrm{n}^{3}-3^{\mathrm{n}}\right)$ $=\sum_{n=1}^{n}\left(n^{3}\right)+\sum_{n=1}^{n}\left(3^{n}\right)$ Note: I. S...
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