Height of a ball(s) =20 m
Acceleration (a)=10 m / s²
Initial velocity (u)=0
Final velocity (v)= ?
According to third equation of motion.
\(v^{2}=u^{2}+2\) as
\(=0+2 \times 10 \times 20  \)
\(v^{2} =0+400  \)
\(v =\sqrt{400}  \)
\(v =\sqrt{20 \times 20}  \)
\(v =20 \mathrm{~m} / \mathrm{s}^{2}\)
Velocity of ball strike the ground = 20 m / s²
According to first law of motion
v = u + at 
20 = 0 + (10) x t 
\(t =\frac{20}{10} \)
v =2 second 
Time taken to strike the ground = 2 second

Pitch scale reading is = 1 mm
Head scale coincidence = 68
Thickness of 5 rupee coin = PSR + (HSC x L.C)
= 1 +(68 x 0.01)
= 1 + 0.68
= 1.68 mm
Thickness of five rupee coin is = 1.68 mm

1. Prevention of mosquito bites by using mosquito nets, mosquito screens, mosquito repellents and ointments.
2. Elimination of breeding places by providing adequate sanitation, underground waste water disposable system and drainage of stagnant water. 
3. Collection of water in any uncovered container such as water tank, pots, flower pots discarded tyres should be avoided.
4. Control of mosquito larvae by spraying oil on stagnated water bodies.
5. Adult mosquitoes can be killed by spraying insecticides.
6. Application of citronella oil or Eucalyptus oil on the exposed skin.

1. It should not be toxic.
2. It should not cause any side effects .
3. It should not affect the receptor tissues .
4. It should not affect the normal physiological activities .
5. It should be effective in its action .
6. Chemicals which satisfy the above criteria only are preferred as drugs.

The intensity of the sound wave depends on
i) Amplitude of the source.
ii) Distance of the observer from the source.
iii) Surface area of the source.
iv) Density of the medium.
v) Frequency of the source.

Fish farm requires different types of pond for the various developmental stages of fish growth, they are
a) Breeding pond:
Healthy and sexually mature male and female fishes are collected and introduced in this pond for breeding. The eggs released by the female are fertilized by the sperm and fertilized eggs float in water as frothy mass.
b) Hatching pits:
The fertilized eggs are transferred to hatching pits for hatching.
c) Nursery ponds:
The hatchlings are transferred from hatching pits after 2 to 7 days. The hatchlings grow into fry and are cultured in these ponds for about 60 days with proper feeding till they reach 2 - 2.5 cm in length.
d) Rearing ponds:
Rearing ponds are used to culture the fry. The fish fry are transferred from nursery pond to rearing ponds and are maintained for about three months till they reach 10 to 15 cm in length. In these rearing ponds, the fry develops into fingerlings.
e) Stocking pond:
The stocking pond is also called as culture pond or production pond. These ponds are used to rear fingerlings upto the markable size. Before releasing the fingerlings the pond is manured with organic manure and inorganic fertilizers.

Q = 400C
t =13 min and 20s
= 13 x 60 + 20 = 780 + 20 = 800s
Current I = \(\cfrac { Q }{ t } =\cfrac { 400 }{ 800 } \) =  0.5A

(a) They have sour taste.
(b) Their aqueous solutions conduct electricity since they contain ions
(c) Acids turns blue litmus red.
(d) Acids react with active metals to give hydrogen gas.
\(Mg+H_2SO_4\rightarrow MgSO_4+H_2\uparrow\)
\(Zn+2Hcl\rightarrow ZnCl_2+H_2\uparrow\)
(e) Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.
\(Na_2CO_3+2HCl\rightarrow 2NaCl+H_2O+CO_2\uparrow\)
\(NaHCO_3+HCl\rightarrow NaCl+H_2O+CO_2\uparrow\)
(f) Acids react with metallic oxides to give salt and water.
\(CaO+H_2SO_4\rightarrow CaSO_4+H_2O\)
(g) Acids react with bases to give salt and water.
\(HCl+NaOH\rightarrow NaCl+H_2O\)

(i) It is the largest digestive gland of the body which is reddish brown in colour.
(ii) It is divided into two main lobes, right and left lobes. The right lobe is larger than the left lobe.
(iii) On the under surface of the liver, gall bladder is present. The liver cells secrete bile which is temporarily stored in the gall bladder.
(iv) Bile is released into small intestine when food enters in it. It has bile salts (sodium glycolate and sodium tauraglycolate) and bile pigments (bilirubin and biliviridin).
(v) Bile salts help in the digestion of fats by bringing about their emulsification (conversion of large fat droplets into small ones).

(i) An alternating current (AC) generator, consists of a rotating rectangular coil ABCD called armature placed between the two poles of a permanent magnet.
(ii) The two ends of this coil are connected to the two slip rings S₁ and S_2. The inner sides of these rings are insulated.
(iii) Two conducting stationary brushes B₁ and B₂ are kept separately on the rings S₁ and S₂ respectively. The two rings S₁ and S₂ are internally attached to an axle.
(iv) The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the external circuit

(v) When the coil is rotated, the magnetic flux linked with the coil changes. This change in magnetic flux will lead to generation of induced current.
(vi) The direction of the induced current, as given by Fleming's Right Hand Rule, is along ABCD in the coil and in the outer circuit it flows from B₂ to B₁.
(vii) During the second half of rotation, the direction of current is along DCBA in the coil and in the outer circuit it flows from B₁ to B₂
(viii) As the rotation of the coil continues, the induced current in the external circuit is changing its direction for every half a rotation of the coil

Cell A : 2 daughter cells
Cell B : 4 daughter cells

Plaster of paris should be stored in a moisture-proof container as it absorbs water from moisture present in air and turn into hard substance (Gypsum).

Principle: An electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming's left hand rule.
Construction: An electric motor consists of the following main parts.
Armature: It is a rectangular coil ABCD having a large number of turns of this insulated copper wire wound over a soft iron core. The armature is placed between the poles of the field magnet and it can be rotated about an axis perpendicular to the magnetic field lines.
Split rings (commutators ): It consists of a cylindrical metal ring split into two halves S1 & S2. As the coil rotates, the split rings also rotate about the same axis of rotation. The function of the split ring is to reverse the direction of current in the coil after every half rotation. Carbon brushes: Two graphite or flexible metal rods maintain a sliding contact with split rings S1 and S2 alternately.
Battery: A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings with split rings S1 and S2 alternately battery flows to the armature coil through the brushes and the split rings.
Working: A simple coil is placed inside two poles of a magnet. Now look at the current carrying conductor segment AB. The direction of the current is towards B, whereas in the conductor segment CD the direction is opposite. As the current is flowing in opposite directions in the segments AB and CD, the direction of the motion of the segments would be in opposite directions according to Fleming's left hand rule. When two ends of the coil experience force in opposite direction, they rotate. If the current flow is along the line ABCD, then the coil will rotate in clockwise direction first and then in anticlockwise direction. If we want to make the coil rotate in anyone direction, say clockwise, then the direction of the current should be along ABCD in the first half of the rotation and along DCBA in the second half of the rotation. When the gap in the split ring commutator is aligned with terminals X and Y there is no flow of current in the coil. But, as the coil is moving, it continues to move forward bringing one of the split ring commutator in contact with the carbon brushes X and Y. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil.

(i) This is a successful group of animals called mammals that adapt themselves readily to new situations and to new food habits.
(ii) The integument is provided with epidermal hairs, sweat, sebaceous and scent glands.
(iii) Mammary glands are the modified integumentary glands.
(iv) The external ear or the pinna is present in most of the mammals.
(v) The heart is four chambered.
(vi) Testes lie outside the body cavity, enclosed in scrotal sacs.
(vii) They give birth to young ones and feed their young with milk.
(viii) Placenta is a characteristic feature.

Between the focus F and the pole P of the mirror.

 Position of Image        Size of Image        Nature of Image
​​​​​​Behind the mirror          Magnified               Virtual and Erect.

Gay Lussac's law of combining volumes.
Gay Lussac's law:
Whenever gases react together, the volumes of the reacting gases as well as the products if they are gases bear a simple whole number ratio provided all the volumes are measured-under similar conditions of temperature and pressure.

Hydrogen combines with oxygen to form water.
2H₂ + 2O₂ \(\longrightarrow \) 2H₂O
(1 volume) + (2 volumes) \(\longrightarrow \) (2 volumes)
                 (1:2:2)
One volume of hydrogen react with two volumes of oxygen to form two volumes of water vapour.
The ratio by volume which gases, bears is 1.2:2 which is a simple number ratio.

Case (a): Zero of the vernier scale and zero of the main scale are coinciding with each other. So there is no zero error.
Case (b): The zero of vernier scale is shifted to the right from the zero of the main scale. It is positive error. The 8th division of vernier scale coincides with one of the main scale divisions. So the positive error = (8×0.01cm) = 0.08 cm.
Case (c): The zero of vernier scale is shifted to the left from the zero of main scale. It is negative error. The 4th division of vernier scale (6th from backward) coincides with one of the main scale divisions. So the negative zero error = ‒(6×0.01cm)= ‒0.06 cm.

No we can't recharge the batteries used in watches, because they are primary cells. The primary cells can't be recharged again. So it is be not possible to recharge them again.