Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
(I) Atomic number: The atomic number of a component is equivalent to the quantity of protons in the nucleus of its molecule.
e.g., Oxygen has 6 protons thus atomic no. = 6.
(ii) Mass number: The mass number of a molecule is equivalent to the quantity of protons and neutrons in its nucleus.
Nucleons = number of protons + number of neutrons
Example: Protons + Neutrons = Nucleus = Mass number = 6 + 6 = 12
(iii) Isotopes: Isotopes are molecules of a similar component which have different mass numbers however same atomic number.
(iv) Isobars: Isobars are molecules having similar mass number however different atomic numbers.
Both calcium and argon have a similar mass number yet unique atomic number.
Two uses of isotopes are:
(I) An isotope of iodine is utilized in the treatment of goiter.
(ii) An isotope of uranium is utilized as a fuel in atomic reactors.
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
How do poriferan animals differ from coelenterate animals?
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?
How are sol, solution and suspension different from each other?
Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood
State any two conditions essential for being free of disease.
What is pasturage and how is it related to honey production?
Convert the following temperature to celsius scale:
a. 300 K b. 573 K.
Which organelle is known as the powerhouse of the cell? Why?
Write the electronic configuration of any one pair of isotopes and isobars.
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s-2, with what velocity will it strike the ground? After what time will it strike the ground?
What are the characteristics of the particles of matter?
What do you mean by buoyancy?