Plastic is used for making a large
Question: Plastic is used for making a large variety of articles of daily use and these articles are very attractive. But it is advised to avoid the use of plastic as far as possible. Why? Solution: The disposal of plastic waste is a major problem because plastic is non-biodegradable, it takes.several years to decompose. Thus, cause environmental pollution. So, we should avoid use of plastics, as for as possible...
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 $C D E$ ...
Read More →Plastic articles are available
Question: Plastic articles are available in all possible shapes and sizes. Can you tell why? Solution: Plastics can be easily moulded, so they are used to make a large variety of articles (or objects) having different shapes and sizes....
Read More →Terrycot is made by mixing
Question: Terrycot is made by mixing two types of fibres. Write the names of the fibres. Solution: Terrycot is made by mixing terylene and cotton....
Read More →A synthetic fibre which looks like silk is obtained
Question: A synthetic fibre which looks like silk is obtained by chemical treatment of wood pulp. It is, therefore, known as artificial silk. What is its common name? Solution: Its common name is rayon. Rayon is often regarded as artificial silk....
Read More →A man 2 metres tall walks away
Question: A man 2 metres tall walks away from a lamp post 5 metres height at the rate of 4.8 km/hr. The rate of increase of the length of his shadow is (a) $1.6 \mathrm{~km} / \mathrm{hr}$ (b) $6.3 \mathrm{~km} / \mathrm{hr}$ (c) $5 \mathrm{~km} / \mathrm{hr}$ (d) $3.2 \mathrm{~km} / \mathrm{hr}$ Solution: LetABbe the lamp post. Suppose at any timet, the manCDbe at a distance ofxkm from the lamp post andym be the length of his shadow CE. Since triangles $A B E$ and $C D E$ are similar, $\frac{A ...
Read More →Cotton is a natural polymer.
Question: Cotton is a natural polymer. What is its chemical name? Solution: Chemical name of natural polymer of cotton is cellulose....
Read More →A man 2 metres tall walks away
Question: A man 2 metres tall walks away from a lamp post 5 metres height at the rate of 4.8 km/hr. The rate of increase of the length of his shadow is (a) $1.6 \mathrm{~km} / \mathrm{hr}$ (b) $6.3 \mathrm{~km} / \mathrm{hr}$ (c) $5 \mathrm{~km} / \mathrm{hr}$ (d) $3.2 \mathrm{~km} / \mathrm{hr}$ Solution: LetABbe the lamp post. Suppose at any timet, the manCDbe at a distance ofxkm from the lamp post andym be the length of his shadow CE. Since triangles $A B E$ and $C D E$ are similar, $\frac{A ...
Read More →The material which is commonly
Question: The material which is commonly used for making kitchen containers is (a) PVC (b) acrylic (c) teflon (d) PET Solution: (d) PET is poly-ethylene terephthalate PET as a plastic is very light weight and is commonly used for making kitchen containers....
Read More →Which of the following groups
Question: Which of the following groups contains all synthetic substances? (a) Nylon, tprylene, wool (b) Cotton, polycot, rayon (c) PVC, polythene, bakelite (d) Acrylic, silk, wool Solution: (c) PVC, polythene and bakelite are synthetic substances....
Read More →Which of the following is not a common
Question: Which of the following is not a common property of plastics? (a) Non-reactive (b) Light in weight (c) Durable (d) Good conductor of electricity Solution: (d) Plastics are non-reactive, light in weight and durable but they do not conduct electricity....
Read More →The diameter of a circle is increasing at the rate of 1 cm/sec.
Question: The diameter of a circle is increasing at the rate of 1 cm/sec. When its radius is , the rate of increase of its area is (a) $\pi \mathrm{cm}^{2} / \mathrm{Sec}$ (b) $2 \pi \mathrm{cm}^{2} / \mathrm{sec}$ (c) $\pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}$ (d) $2 \pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}^{2}$ Solution: (c) $\pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}$ Let $D$ be the diameter and $A$ be the area of the circle at any time $t .$ Then, $A=\pi r^{2}$ (where $r$ is the radius of the cic...
Read More →The most suitable material for
Question: The most suitable material for the preparation of handles of cooking utensils is (a) polythene (b) PVC (c) nylon (d) bakelite Solution: (d) Bakelite is used for making the handles of various cooking utensils because it is a poor conductor of heat and does not become soft on getting heated....
Read More →The diameter of a circle is increasing at the rate of 1 cm/sec.
Question: The diameter of a circle is increasing at the rate of 1 cm/sec. When its radius is , the rate of increase of its area is (a) $\pi \mathrm{cm}^{2} / \mathrm{Sec}$ (b) $2 \pi \mathrm{cm}^{2} / \mathrm{sec}$ (c) $\pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}$ (d) $2 \pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}^{2}$ Solution: (c) $\pi^{2} \mathrm{~cm}^{2} / \mathrm{sec}$ Let $D$ be the diameter and $A$ be the area of the circle at any time $t .$ Then, $A=\pi r^{2}$ (where $r$ is the radius of the cic...
Read More →The material similar to silk
Question: The material similar to silk in appearance is (a) nylon (b) rayon (c) polyester (d) terylene Solution: (b) Rayon resembles silk in appearance, therefore, rayon is also called artificial silk....
Read More →Which is a thermosetting plastic?
Question: Which is a thermosetting plastic? (a) Melamine (b) Polythene (c) PVC (d) Nylon Solution: (a) Melamine is a thermosetting plastic which when moulded once, cannot be softened by heating....
Read More →Polycot is obtained by mixing
Question: Polycot is obtained by mixing (a) nylon and wool (b) polyester and wool (c) nylon and cotton (d) polyester and cotton Solution: (d) Polycot is obtained by mixing polyester and cotton. Polycot = polyester + cotton...
Read More →Which of the following
Question: Which of the following is a source of rayon? (a) Wool (b) PET (c) Wood pulp (d) Silk Solution: (c) Wool pulp Rayon is obtained by the chemical treatment of wool pulp (which contains cellulose)....
Read More →The sum of first three terms of a GP is
Question: The sum of first three terms of a GP is $\frac{39}{10}$ and their product is $1 .$ Find the common ratio and these three terms. Solution: Let the first three terms of G.P. be $\frac{a}{r}, a, a r$ It is given that $\frac{a}{r} \times a \times a r=1$ $\Rightarrow a^{3}=1$ $\Rightarrow a=1$ And $\frac{a}{r}+a+a r=\frac{39}{10}$ $\Rightarrow a\left(\frac{1}{r}+1+r\right)=\frac{39}{10}$ $\Rightarrow\left(\frac{1}{r}+1+r\right)=\frac{39}{10} \ldots(a=1)$ $\Rightarrow\left(\frac{1}{r}+r\righ...
Read More →The radius of a circular plate is increasing at the rate of 0.01 cm/sec.
Question: The radius of a circular plate is increasing at the rate of $0.01 \mathrm{~cm} / \mathrm{sec}$. The rate of increase of its area when the radius is $12 \mathrm{~cm}$, is (a) $144 \pi \mathrm{cm}^{2} / \mathrm{sec}$ (b) $2.4 \pi \mathrm{cm}^{2} / \mathrm{sec}$ (c) $0.24 \pi \mathrm{cm}^{2} / \mathrm{sec}$ (d) $0.024 \pi \mathrm{cm}^{2} / \mathrm{sec}$ Solution: (c) $0.24 \pi \mathrm{cm}^{2} / \mathrm{sec}$ Let $r$ be the radius and $A$ be the area of the circular plate at any time $t .$...
Read More →The ratio of the sum of first three terms is to that of first six terms of a GP
Question: The ratio of the sum of first three terms is to that of first six terms of a GP is 125 : 152. Find the common ratio. Solution: The first three terms of a G.P. are:a,ar,ar2 The first six terms of a G.P. are:a,ar, $a r^{2}, a r^{3}, a r^{4}, a r^{5}$ It is given that the ratio of the sum of first three terms is to that of first six terms of a GP is $125: 152$. $\Rightarrow a+a r+a r^{2}=125 x \ a+a r+a r^{2}+a r^{3}+a r^{4}+a r^{5}=152 x$ $\Rightarrow a+a r+a r^{2}+r^{3}\left(a+a r+a r^{...
Read More →Pick the synthetic fibre
Question: Pick the synthetic fibre out of the following. (a) Cotton (b) Nylon (c)Jute (d)Wool Solution: (b) Nylon Is a synthetic fibre. It is made without using any natural raw material. Cotton, jute and wool are natural fibres....
Read More →The equation of motion of a particle
Question: The equation of motion of a particle is $s=2 t^{2}+\sin 2 t$, where $s$ is in metres and $t$ is in seconds. The velocity of the particle when its acceleration is $2 \mathrm{~m} / \mathrm{sec}^{2}$, is (a) $\pi+\sqrt{3} \mathrm{~m} / \mathrm{sec}$ (b) $\frac{\pi}{3}+\sqrt{3} \mathrm{~m} / \mathrm{sec}$ (c) $\frac{2 \pi}{3}+\sqrt{3} \mathrm{~m} / \mathrm{sec}$ (d) $\frac{\pi}{3}+\frac{1}{\sqrt{3}} \mathrm{~m} / \mathrm{sec}$ Solution: (b) $\frac{\pi}{3}+\sqrt{3} \mathrm{~m} / \mathrm{sec...
Read More →The second term of a GP is 24 and its fifth term is 81.
Question: The second term of a GP is 24 and its fifth term is 81. Find the sum of its first five terms. Solution: Given: second term of a GP is 24 and its fifth term is 81. To find: sum of first five terms of the G.P. $a r=24 \ a r^{4}=81$ dividing these two terms we get: $\Rightarrow \frac{\mathrm{ar}^{4}}{\mathrm{ar}}=\frac{81}{24}$ $\Rightarrow \Gamma^{3}=\frac{27}{8}$ Taking cube root on both the sides we get, $\Rightarrow r=\frac{3}{2}$ Substituting this value of r in ar = 24 we get $a=24 /...
Read More →If the solve the problem
Question: If $s=t^{3}-4 t^{2}+5$ describes the motion of a particle, then its velocity when the acceleration vanishes, is (a) $\frac{16}{9}$ unit / sec (b) $-\frac{32}{3}$ unit/sec (c) $\frac{4}{3}$ unit/sec (d) $-\frac{16}{3}$ unit/sec Solution: (d) $-\frac{16}{3}$ unit / sec According to the question, $s=t^{3}-4 t^{2}+5$ $\Rightarrow \frac{d s}{d t}=3 t^{2}-8 t$ $\Rightarrow \frac{d^{2} s}{d t^{2}}=6 t-8$ $\Rightarrow 6 t-8=0$ $\left[\right.$ As velocity deminishes, then $\left.\frac{d^{2} s}{...
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