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Work, Power And Energy — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceWork, Power And Energy4 Marks
Question
Lift an object through a certain height. The object can now do work. It begins to fall when released. This implies that it has acquired some energy. If raised to a greater height it can do more work and hence possesses more energy. From where did it get the energy? In the above situations, the energy gets stored due to the work done on the object. The energy transferred to an object is storedas potential energy if it is not used to cause a change in the velocity or speed of the object.An object increases its energy when raisedthrough a height. This is because work isdone on it against gravity while it is being raised. The energy present in such an objectis the gravitational potential energy.The gravitational potential energy of anobject at a point above the ground is definedas the work done in raising it from the ground by height hto that point against gravity.Let the work done on the object against gravity beW. That is,
work done, $W$ = force $\times $ displacement
$= mg \times h$
Therefore potential energy $(PE)= mg*h.$
(i) Energy possessed by body due to its position is called
$(a)$ Potential energy
$(b)$ Kinetic energy
$(c)$ Nuclear energy
$(d)$ None of these
(ii) SI unit of potential energy is
$(a)$ Joule$(J)$
$(b)$ Newton meter$(N-m)$
$(c)$ both $a$ and$ b$
$(d)$ None of these
(iii)You do work while winding the key of a toy car. The energy transferred to the spring inside is stored as
$(a)$ Potential energy
$(b)$ Kinetic energy
$(c)$ Nuclear energy
$(d)$ None of these
(iv)Find the energy possessed by an object of mass 5kg when it is at a height of 10 m above the ground. Given, $g = 9.8 m/s^2.$
(v)Find the work done by Gravity on an object of mass 5 kg which moves from height 10m to ground when it is released from height of 10 m. Given, $g = 9.8 m/s^2.$
✓

Answer

$(i)$ $a$
$(ii)$ $c$
$(iii)$ $a$
$(iv)$ we have potential energy as
$= mg \times h$
$=5 \times 9.8 \times 10$
$=490 J$
$(v)$ work done, $W$ = force \times displacement
$= mg \times h$
$= 5 \times 9.8 \times 10$
$=490 J$

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Elemental oxygen is normally found in the form of a diatomic molecule. However, in the upper reaches of the atmosphere, a molecule containing three atoms of oxygen is found. This would mean a formula of $O3$ and this is called ozone. Unlike the normal diatomic molecule of oxygen, ozone is poisonous and we are lucky that it is not stable nearer to the Earth’s surface. But it performs an essential function where it is found. It absorbs harmful radiations from the Sun. This prevents those harmful radiations from reaching the surface of the Earth where they may damage many forms of life. Recently it was discovered that this ozone layer was getting depleted. Various man-made compounds like $CFCs$ (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) were found to persist in the atmosphere. Once they reached the ozone layer, they would react with the ozone molecules. This resulted in a reduction of the ozone layer and recently they have discovered a hole in the ozone layer above the Antarctica. It is difficult to imagine the consequences for life on Earth if the ozone layer dwindles further, but many people think that it would be better not to take chances. These people advocate working towards stopping all further damage to the ozone layer.
(1) Identify the correct statement
Statement $1$ – Ozone is poisonous.
Statement $2$ – Absorbs harmful radiations from the Sun
Statement $3$ – Ozone prevents those harmful radiations from reaching the surface of the Earth.
Statement $4$ – Molecule containing three atoms of oxygen is termed as ozone.
$(a)$ Both $1$ & $4$
$(b)$ Both $2$ & $4$
$(c)$ Only $3$
$(d)$ All of the above
(2) The molecule containing three atoms of oxygen is termed as
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$(b)$ Ozone
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$(d)$ None of above
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$(d) O4$
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(c) Has abundant matrix
(d) None of these
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(a) Skin and muscles
(b) Blood vessels and nerves
(c) Both a & b
(d) None of these
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(a) Ligament
(b) Cartilage
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(d) Blood
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i. What type of cell are present where absorption and secretion occur?
ii. Skin helps in the protection of body explain?
iii. How cilia clear mucus?
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$(a)$ Simple permanent tissue
$(b)$ Complex permanent tissue
$(c)$ Simple Meristematic tissue
$(d)$ Complex Meristematic tissue
(2) Xylem and phloem are examples of
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$(b)$ Simple tissue
$(c)$ Protective tissue
$(d)$ Complex tissue
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$(b)$ Chlorenchyma
$(c)$ Sclerenchyma
$(d)$ Parenchyma
(4) What is mean by Differentiation?
(5) Enlist the type of parenchyma tissue.
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$i.$ What do mean by the term Solubility?
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$(a)$ $J.J.$ Thomson
$(b)$ John Dalton
$(c)$ $E.$ Rutherford
$(d)$ Neilsbhore
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$(b)$ Molecule
$(c)$ Atom
$(d)$ Protons
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Statement $2$ – The electrons revolve around the nucleus in circular paths.
Statement $3$ – Nearly all the mass of an atom resides in the nucleus.
Statement $4$ – The size of the nucleus is very small as compared to the size of the atom.
$(a)$ Only $2$
$(b)$ Both $3$ & $4$
$(c)$ Both $1$ & $2$
$(d)$ All of the above
(4) Write the features of Rutherford’s nuclear model of an atom?
(5) Define Nucleus.
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