Metals are generally solid.
Question: Metals are generally solid. Which of the following metals is in the liquid state at room temperature? (a) Mercury (b) Silver (c) Aluminium (d) Sodium Solution: (a) Mercury metal is in the liquid state at room temperature....
Read More →The rate of change
Question: The rate of change of $\sqrt{x^{2}+16}$ with respect to $\frac{x}{x-1}$ at $x=3$ is__________________ Solution: Let $u(x)=\sqrt{x^{2}+16}$ and $v(x)=\frac{x}{x-1}$. $u(x)=\sqrt{x^{2}+16}$ Differentiating both sides with respect to $x$, we get $\frac{d u}{d x}=\frac{1}{2 \sqrt{x^{2}+16}} \times 2 x=\frac{x}{\sqrt{x^{2}+16}}$ $v(x)=\frac{x}{x-1}$ Differentiating both sides with respect to $x$, we get $\frac{d v}{d x}=\frac{(x-1) \times 1-x \times 1}{(x-1)^{2}}=-\frac{1}{(x-1)^{2}}$ Now, ...
Read More →Metals are generally hard.
Question: Metals are generally hard. Which of the following metals is an exception ! and can be cut with a knife? (a) Iron (b) Sodium (c) Gold (d) Magnesium Solution: (b) Metals are generally hard. This means that most of the metals cannot be cut easily. But sodium metal is soft and can be easily cut with a knife....
Read More →Materials which can be drawn into wires
Question: Materials which can be drawn into wires are called ductile. Which of the following is not a ductile material? (a) Silver (b) Copper (c) Sulphur (d) Aluminium Solution: (c) Ductility is a characteristic property of metals. Sulphur is a non-metal, so it is not ductile. When stretched, sulphur break into pieces and do not form wires....
Read More →Boojho has learnt that non-metals on beating
Question: Boojho has learnt that non-metals on beating with a hammer are generally broken into pieces. Which of the following is non-metal? (a) Iron nail (b) Aluminium wire (c) Copper plate (d) Piece of coal Solution: (d) Piece of coal is a non-metal which broke into small pieces when hammered....
Read More →The substance that will be flattened
Question: The substance that will be flattened on beating with a hammer is (a) crystal of iodine (b) lump of sulphur (c) piece of coal 4 (d) zinc granule Solution: (d) Metals can be beaten into thin sheets (or flattened) with a hammer. Non-metals break into small pieces when hammered. So, zinc granule will be flattened on beating with a hammer....
Read More →Which of the following
Question: Which of the following is not a metal? (a) Copper (b) Sulphur (c) Aluminium (d) Iron Solution: (b) Copper, aluminium and iron are metals but sulphur is not a metal....
Read More →A cylindrical tank of radius 10 m is being filled
Question: A cylindrical tank of radius 10 m is being filled with wheat at the rate of 314 cubic metre per hour. Then the depth of the wheat is increasing at the rate of (a) $1 \mathrm{~m} / \mathrm{hr}$ (b) $0.1 \mathrm{~m} / \mathrm{hr}$ (c) $1.1 \mathrm{~m} / \mathrm{hr}$ (d) $0.5 \mathrm{~m} / \mathrm{hr}$ Solution: (a) 1 m/hr Let $r, h$ and $V$ be the radius, height and volume of the cylinder at any time $t .$ Then, $V=\pi r^{2} h$ $\Rightarrow \frac{d V}{d t}=\pi r^{2} \frac{d h}{d t}$ $\Ri...
Read More →A cylindrical tank of radius 10 m is being filled
Question: A cylindrical tank of radius 10 m is being filled with wheat at the rate of 314 cubic metre per hour. Then the depth of the wheat is increasing at the rate of (a) $1 \mathrm{~m} / \mathrm{hr}$ (b) $0.1 \mathrm{~m} / \mathrm{hr}$ (c) $1.1 \mathrm{~m} / \mathrm{hr}$ (d) $0.5 \mathrm{~m} / \mathrm{hr}$ Solution: (a) 1 m/hr Let $r, h$ and $V$ be the radius, height and volume of the cylinder at any time $t .$ Then, $V=\pi r^{2} h$ $\Rightarrow \frac{d V}{d t}=\pi r^{2} \frac{d h}{d t}$ $\Ri...
Read More →Despite being very useful,
Question: Despite being very useful, it is advised to restrict the use of plastic. Why is it so? Can you suggest some methods to limit its consumption? Solution: It is advised to restrict the use of plastic because of the following reasons: The articles mades of plastics are non-biodegradable. They do not decompose (or rot) easily. This causes a great problem in the disposal of plastic wastes. The burning of plastic wastes gives out harmful gases which pollute the air. So, it is not advisable to...
Read More →Write the importance of synthetic
Question: Write the importance of synthetic polymers in our life. Solution: The importance of synthetic polymers in our life are as follows: Nylon It is used for making ropes for rock climbing, fishing nets, raincoats, parachutes and tyre cords, etc. Acrylic It is used for sweaters, track suits, linings for boots and gloves and In furnishing fabrics and carpets. Terylene It is used in textile industry to make clothes like sarees, tapestry and dress material. It is also mixed with natural fibre l...
Read More →State whether the following statements are True/False.
Question: State whether the following statements are True/False. The fabric tery wool is obtained by mixing terylene and wool. Synthetic fibre do not melt on heating. It is risky to wear synthetic clothes while working in the kitchen. Most of the plastics are biodegradable. Solution: True False, synthetic fibres melt on heating. True, a disadvantage as synthetic fibre is that they melt on heating. False, most of the plastics are non-biodegradable....
Read More →In a sphere the rate of change of volume is
Question: In a sphere the rate of change of volume is(a) times the rate of change of radius(b) surface area times the rate of change of diameter(c) surface area times the rate of change of radius(d) none of these Solution: (c) surface area times the rate of change of radius LetrbetheradiusandVbethevolumeofsphereatanytimet.Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{d V}{d t}=\frac{4}{3}\left(3 \pi r^{2}\right)\left(\frac{d r}{d t}\right)$ $\Rightarrow \frac{d V}{d t}=4 \pi r^{2}\left(\fra...
Read More →Unscramble the jumbled materials.
Question: Unscramble the jumbled materials. words given below, related to synthetic (a) Anory (b) Lopmery (c) Relyteen (d) Laspict (e) Yespolter (f) Felton Solution: (a) Rayon (b) Polymer (c) Terylene (d) Plastic (e) Polyester (f) Teflon...
Read More →In a sphere the rate of change of volume is
Question: In a sphere the rate of change of volume is(a) times the rate of change of radius(b) surface area times the rate of change of diameter(c) surface area times the rate of change of radius(d) none of these Solution: (c) surface area times the rate of change of radius LetrbetheradiusandVbethevolumeofsphereatanytimet.Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{d V}{d t}=\frac{4}{3}\left(3 \pi r^{2}\right)\left(\frac{d r}{d t}\right)$ $\Rightarrow \frac{d V}{d t}=4 \pi r^{2}\left(\fra...
Read More →Fill in the blanks.
Question: Fill in the blanks. A polymer is a chain of many small units joined together which arecalled. The synthetic fibres are also known as.fibres. The first fully synthetic fibre was . A fibre similar to wool is. A plastic used for making crockery is. Solution: monomers man-made nylon acrylic melamine...
Read More →PVC (polyvinyl chloride) is a thermoplastic
Question: PVC (polyvinyl chloride) is a thermoplastic and is used for making toys, chappals, etc. Bakelite is a thermosetting plastic and is used for making electrical switches, handles of various utensils, etc. Can you write the major difference between these two types of plastics? Solution: Thermoplastics get deformed easily on heating and can be bent easily on heating. On the other hand, thermosetting plastics when moulded once cannot be softened on heating. Thermoplastics Polythene and PVC T...
Read More →A lady went to the market to buy a blanket.
Question: A lady went to the market to buy a blanket. The shopkeeper showed her blankets made up of acrylic fibres as well as made up of wool. She preferred to buy an acrylic blanket. Can you guess why? Solution: Acrylic blankets are cheap, light in weight, more durable and are available in variety of colours and designs. They can be easily washed at home....
Read More →Rohit took with him some nylon ropes,
Question: Rohit took with him some nylon ropes, when he was going for rock climbing. Can you tell why he selected nylon ropes instead of ropes made up of cotton or jute? Solution: Nylon ropes are strongfelastic and lighter as compared to cotton and jute ropes. A nylon thread is actually stronger than a steel wire of similar thickness....
Read More →A bucket made of plastic does not
Question: A bucket made of plastic does not rust like a bucket made up of iron. Why? Solution: Plastic is non-reactive material. When left exposed to moisture and air, it does not react with air and water which are essential for corrosion, therefore does not rust....
Read More →In a sphere the rate of change of volume is
Question: In a sphere the rate of change of volume is(a) times the rate of change of radius(b) surface area times the rate of change of diameter(c) surface area times the rate of change of radius(d) none of these Solution: (c) surface area times the rate of change of radius Let $r$ be the radius and $V$ be the volume of sphere at any time $t .$ Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{d V}{d t}=\frac{4}{3}\left(3 \pi r^{2}\right)\left(\frac{d r}{d t}\right)$ $\Rightarrow \frac{d V}{d t...
Read More →In a sphere the rate of change of volume is
Question: In a sphere the rate of change of volume is(a) times the rate of change of radius(b) surface area times the rate of change of diameter(c) surface area times the rate of change of radius(d) none of these Solution: (c) surface area times the rate of change of radius Let $r$ be the radius and $V$ be the volume of sphere at any time $t .$ Then, $V=\frac{4}{3} \pi r^{3}$ $\Rightarrow \frac{d V}{d t}=\frac{4}{3}\left(3 \pi r^{2}\right)\left(\frac{d r}{d t}\right)$ $\Rightarrow \frac{d V}{d t...
Read More →Select the articles from the following
Question: Select the articles from the following list which are biodegradable. (a) Paper (b) Woollen clothes (c) Wood (d) Aluminium can (e) Plastic bag (f) Peels of vegetables Solution: The biodegradable articles are: (a) paper (b) woollen clothes (c) wood (f) peels of vegetables...
Read More →Why is it not advisable to burn
Question: Why is it not advisable to burn plastic and synthetic fabrics? Solution: Burning of plastics and synthetic fabrics produces lots of poisonous gases causing air pollution. So, it is not advisable to burn plastic and synthetic fibres....
Read More →A man of height 6 ft walks at a uniform speed of 9 ft/sec from a lamp fixed at 15 ft height.
Question: A man of height 6 ft walks at a uniform speed of 9 ft/sec from a lamp fixed at 15 ft height. The length of his shadow is increasing at the rate of (a) $15 \mathrm{ft} / \mathrm{sec}$ (b) $9 \mathrm{ft} / \mathrm{sec}$ (c) $6 \mathrm{ft} / \mathrm{sec}$ (d) none of these Solution: (c) $6 \mathrm{ft} / \mathrm{sec}$ LetABbe the lamp post. Suppose at any timet,the manCDbe at a distance ofxkm from the lamp post andyft be the length of his shadow CE. Since the triangles $A B E$ and $C D E$ ...
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