Question 4

Describe Bohr’s model of the atom.

Answer

Bohr's model of the molecule

(1) Atoms have a nucleus in the middle.

(2) Electrons rotate around the nucleus.

(3) Certain exceptional circles known as discrete circles of electrons are permitted inside the molecule.

(4) While rotating in discrete circles the electrons don't transmit energy.

(5) These circles or shells are called energy levels.

(6) These circles or shells are represented by the letters K, L, M, N or the numbers n = 1, 2, 3, 4

- Q:-
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? - Q:-
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.

- Q:-
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? - Q:-
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? - Q:-
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? - Q:-
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?

- Q:-
How do poriferan animals differ from coelenterate animals?

- Q:-
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. - Q:-
What happens to the force between two objects, if

(i) the mass of one object is doubled?

(ii) the distance between the objects is doubled and tripled?

(iii) the masses of both objects are doubled? - Q:-
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?

- Q:-
A hockey ball of mass 200 g travelling at 10 m s

^{-1}is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s^{-1}. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick. - Q:-
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? - Q:-
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? - Q:-
A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h

^{-1}in 10 minutes. Find its acceleration. - Q:-
How are sol, solution and suspension different from each other?

- Q:-
How do poriferan animals differ from coelenterate animals?

- Q:-
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? - Q:-
Give three examples of the range of variations that you see in life-forms around you.

- Q:-
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

- Q:-
Which wave property determines

(a) loudness, (b) pitch?

- NCERT Chapter

Copyright © 2022 saralstudy.com. All Rights Reserved.