You are provided with a fine white colou | Class 9 Science Chapter Atoms and Molecules, Atoms and Molecules NCERT Solutions

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?

Differentiate between homogeneous and heterogeneous mixtures with examples.

Which do you think is a more basic characteristic for classifying organisms?

(a) the place where they live.
(b) the kind of cells they are made of. Why?

Gravitational force on the surface of the moon is only 1/6 as strong as gravitational force on the earth. What is the weight in newtons of a 10 kg object on the moon and on the earth?

Diagrammatically show the difference between the three types of muscle fibres.

What are the differences between amphibians and reptiles?

An electron moving with a velocity of 5 × 10⁴ m s^-1 enters into a uniform electric field and acquires a uniform acceleration of 10⁴ m s^–2 in the direction of its initial motion.
(i) Calculate the time in which the electron would acquire a velocity double of its initial velocity.
(ii) How much distance the electron would cover in this time?

Suggest some preventive measures for the diseases of poultry birds.

Draw a plant cell and label the parts which
(a) determines the function and development of the cell.
(b) packages materials coming from the endoplasmic reticulum.
(c) provides resistance to microbes to withstand hypotonic external media without bursting.
(d) is site for many biochemical reactions necessary to sustain life.
(e) is a fluid contained inside the nucleus.

Why are the ceilings of concert halls curved?

Define the term hybridization and photoperiod.