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## Tuesday, February 21, 2012

### CBSE PHYSICS:Work, Energy and Power IX Physics assignment

CBSE PHYSICS: CBSE Work, Energy and Power IX Physics assignment
1. Under what conditions work is said to be done?
2. Derive the formula for work done by a constant force
3. Give few examples where energy is possessed by a body due to its change in shape.
4. State and prove the law of conservation of energy.
5. Is it possible that force is acting on a body but still work done is zero? Explain.
6. A rocket of mass 3x106 kg takes off from a launching pad and acquires a vertical velocity of 1km/s at an altitude of 25 km. calculate (a) the potential energy and (b) the kinetic energy. (g = 9.8m/s2)
7. If a man lifts a load up with the help of a rope such that it raises the load of mass 50kg to a height of 20m in 100 sec. Find the power of man
8. A ball is dropped from a height of 5m. Find the velocity of the ball just before it reaches the ground. Do you require the value of mass to find the velocity?
9. Two persons A and B do same amount of work. The person A does that work in t 1 sec and the person b in t2sec. Find the ratio of power delivered by them.
10. Why do our hands become warm when rubbed against each other? Explain.
11. The kinetic energy of a body of mass 15 kg is 30J. What is its momentum?
12. Give an example for each of the following energy conversion: (1) electrical energy to kinetic energy. (2) Chemical energy to electrical energy (3) sound energy to electrical energy
13. Two bodies have same momentum. Which will have greater kinetic energy- heavier body or lighter body?
14. An electric bulb of 60w is used for 6h per day .Calculate the units of energy consumed in one day by the bulb.
15. A boy of mass 50kg runs up to a stair case of 45 steps in 9s. If the height of a step is 15cm, find his power. (g= 10m/s2)
16. Two particles of masses 1g and 2g have equal momentum. Find the ratio between their kinetic energies?
17. What will be the work done by the string, when a stone is tied to a string and whirled in a circle?
18. A locomotive exerts a force of 7500N and pulls a train through 1.5 km. How much work is done by locomotive?
19. What work a boy of mass 50kg will do in order to increase running speed from 9km/h to 18km/h.
20. The speed of a moving body is halved. What is the change in its K.E.?
21. State the energy changes taking place in the following cases: (1) A car moves up a hilly road.(2) a stone projected vertically upward returns
22. When we cut a log of wood with a saw it becomes warm, why?
23. If an electric iron of 1200W is used for 30 minutes everyday, find electric energy consumed in the month of April.
CBSE Chapter: Structure of an Atom IX Chemistry assignment
Q.1. What are Canal rays?
Q.2. On the basis of Thomson's model of an atom explain how the atom is neutral as a whole.
Q.3 Draw a sketch of Bohr's model of an atom with three shells.
Q.4. Helium atom has atomic mass of 4u and has two protons in the nucleus. How many neutrons does it have?
Q.5. If the K and L shells of an atom are full, then what would be the number of electrons in the atom?
Q.6. If the number of electrons in an atom is 8 and the number of protons is also 8, then;
(i) What would be the atomic number of the atom? (ii) What is the charge on the atom?
Q.7. Na+ ion has completely filled k and L shells. Explain.
Q.8. The average atomic mass of a sample of element X is 16.2 u. What are the percentages of isotopes 16 X8 and 18 X8 in the sample?
Q.9. If Z=3, what would be the valency of the element ? Also, name the element.
Q. 10. Composition of the nuclei of two atomic species X and Y are given as under
X Y
Protons = 6 6
Neutrons = 6 8
Give the mass numbers of X and Y. What is the relation between the two species ?
Q.11. Why do the elements helium, neon and argon have zero valency ?
Q.12. Why do elements which exist as isotopes have fractional atomic masses ?
Q.13. Are mass number and atomic mass of an element equal in all respects?
Q.14. The element ALuminium is written by the symbol 27 13 Al. Write the number of protons, electrons and neutrons present in it.
Q.15. The electronic configuration of an element Z is 2, 8, 6. How many electrons does it require to have a stable configuration?
Q.16. Two atoms A and B have the following composition:
Atom A Atom B
17 protons 17 protons
18 neutrons 20 neutrons
What are their mass numbers ? What is the relation between the species ?Q.17. The composition of two atomic particles is given :
X Y
Protons 8 8
Neutrons : 8 9
Electrons : 8 8
(i) What is the mass number of X ? (ii) What is the mass number of Y ?
Q.18. Briefly describe the features of the Rutherford Model of an atom. what are the drawbacks ?
Q.19. How do isotopes and isobars differ? Write three applications of isotopes.
Q. 20. What observations in scattering experiment led Rutherford to make the following conclusions:
(i) Most of the space in an atom is empty. (ii) Whole mass of an atom is present in its centre.
(iii) Nucleus is positivity charged.
Q.21. Explain why did Rutherford select a gold foil innhis alpha-ray scatering experiment.
Q.22. The atom of an element 'A' has three electrons in the outermost shell. It loses one of these to the atom of another element 'B'. What will be the nature and value of charge on the ion which results from 'A'
Q.23.The atomic numbers of atoms of two elements are 18 and 20 respectively and their mass numbers are 40. What is the name that can be given to such pairs of atoms. Will they have same chemical characteristics?
Q. 24. Give reasons for the following:
(a) Isotopes of an element are chemically similar.
(b) An atom is electrically neutral
(c) Noble gases show least reactivity
(d) Nucleus of an atom is heavy and positively charged.
(e) Ions are more stable than atoms.
Q.25. which of the two will be chemically more reactive; element X with atomic number 17 or element with atomic number 16 ?
Q.26. an unknown species X has 17 protons and 18 electrons. Predict its nature.