CLASS 8 SET-4
HINTS AND SOLUTIONS 1.
(B) : Gravitational force and frictional force will act when a rocket is red upward to launch a satellite in its orbit.
2.
(C) : If all forces acting on a object are balanced, then it will move with same s ame velocity.
3.
(B) : Spe Speed =
2 × Distance
⇒ Distance = 4.
, 1250 =
Time 1250 × 1.25 2
1.25
( R). ). 15. (C) : Incident ray ( P ) is parallel to emergent ray ( R
= 781 781.25 m
5.
(D) : If temperature of air increase, then the time period of sound waves in air will be changed and also frequency will be changed.
6.
(A) : ∠i = 40° =
∠r
P
13. (C) : When current is passed through molten sodium chloride, sodium is deposited at the negative electrode and the chlorine gas is formed at positive electrode. 14. (C)
2 × Distance
(A) : Sound waves cannot travel in space because sound waves need a medium for propagation. In space, there is vacuum.
M
12. (C)
16. (C) : When more than half of moon is visible it is gibbous moon and when small portion of moon is visible to us after two three days of new moon is called crescent moon. 17. (B)
Negative ve charge charge means excess of electrons electrons and positive positive 18. (B) : Negati charge means deciency of electrons. Here electroscope (i) is negatively charged, means it has more electrons, so when it is made in contact with electroscope (ii) which is positively charged, electrons will ow from electroscope (i) to (ii). 19. (D) : A coating of zinc is deposited on iron to protect it from corrosion and formation of rust.
O 60°
40°
20. (B) : In hot and humid weather, these clothes stick to the
body and make us feel uncomfortable. R
21. (D) : Zn + 2HCl → ZnCl2 + H2↑ Sulphur is a non–metal. Non–metals do not react with acids.
Q
N
OPQ = = ∠OPQ
90° – 40° = 50° = 180° – (50° + 60°) = 180° – 110° = 70° ∠OQP = \ ∠ PQR = 90° – 70° = 20° { QR QR is is normal ray to mirror} 7.
(B) : The focal length is the distance between optical centre and the focus of a lens therefore it is Q.
8.
(B) : The image formed by a plane mirror is always upright, virtual, of same size and laterally inverted.
9.
(B)
10. (D) : Pr essure essure =
Force Area
If force = 2 f and
Area =
2 f 6 f = A A 3 Dividing eqn (i) by eqn (ii) P ′
=
1 6
⇒ P ′ = 6 P
Class 8 | Level-2
24. (B) : Because of their light weight, lower price, good strength, easy handling they are used for storing food, chemicals in industry etc. Plastic are non–biodegradable and takes several years to decompose. They are not environment friendly and cause pollution. 2
+ H2
Iron
Fe 2
3.xH2 Rust
Humid air
26. (D)
⇒ P =
\ P ′ =
P
23. (B)
25. (D) : Fe +
Force
Area Force = Pressure P ressure × Area = 90 × 2 × 3 = 540 N
11. (C) : Pr essure essure =
22. (A)
f A
…(i)
A 3 …(ii)
27. (A) : The heat supplied to paper cup is transferred tr ansferred to water by conduction. So, in presence of water the ignition temperatur e of paper is not reached. Hence, it does not burn. 28. (B) : Fabric made up of polyester does not get wrinkled easily. Melamine is a thermosetting plastic, it resists re and can tolerate heat better than other plastics. 29. (D) 30. (B) : Phosphorus is a very reactive non–metal. It catches re if exposed to air. To prevent the contact of phosphorus with oxygen, it is stored in water.
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31. (B) : Picture X shows a thresher, used to separate grains from harvested crop. Picture Y shows a combine which used both for harvesting and threshing.
controlled by thyroxine produced from thyroid gland, whose formation requires appropriate iodine concentration in the surrounding water.
32. (D)
43. (B)
33. (B)
44. (D) : W represents the sperm ducts, X is Urethra, Y is testes and Z represents Penis. Testes serves the function of producing male gametes called sperms.
34. (B) : The given gure is of a bacteriophage. Bacteriophage is the virus that infects the bacteria. It cannot multiply on its own. 35. (C) : Bacteria are responsible for causing typhoid, cholera, pneumonia, etc in human beings. 36. (D) 37. (C) : The animal shown in the given picture is a lion-tailed macaque which is an example of an endangered species. The members of this species are not likely to survive and will soon become extinct, if the same causative factors continue. 38. (B) : Prohibition of hunting of listed threatened species and control and management of captive breeding are objectives of Wildlife Protection Act. 39. (A) 40. (A) : Adrenal glands are present on the top of each kidney which produce a hormone adrenaline. 41. (A) : Paramoecium has two nuclei, larger macronucleus and a small micronucleus. Brain cell has only one nuclei. RBCs of mammals are enucleated, i.e., do not contain any nucleus. 42. (C) : In insects such as butterflies, metamorphosis is controlled by insect hormones. Metamorphosis in frogs is
45. (B) : Yeast reproduces asexually by budding. Hy dr a also reproduces by budding. Starsh reproduces through regeneration. Amoeba reproduces by binary ssion and atworms by fragmentation. 46. (B) : Since density of block is less than that of water, therefore it will oat. 47. (C) : Pressure, P =
Force Area
=
mg A × h × ρ × g = A A
P = 16 × 1000 × 10 = 16 × 104 Pa 48. (D) 49. (D) : P is cytoplasm. S represents Golgi apparatus which is a secretory organelle. Endoplasmic reticulum labelled as R offer a large surface area for various enzymes to function and is not involved in packaging. Q represents a ribosome and T is mitochondria which is absent in RBCs of human. 50. (B) : W — Muscular wall of uterus X — Placenta Y — Umbilical cord Z — Amnion The embryo within the mother’s uterus obtains nutrients
and oxygen from mother’s blood through placenta.
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Class 8 | Level-2
