Gravitation — Science STD 9 — Question

What is the force of gravity on a body of mass 150kg lying on the surface of the earth?
(Mass of earth = 6 × 10²⁴kg; Radius of earth = 6.4 × 10⁶m; G = 6.7 × 10^-11Nm²/kg²)

A boy tries to push a truck parked on the roadside.The truck does not move at all. Another boy pushes a bicycle moves through a certain distance. In which case was the work done more: on the truck or on the bicycle? Give a reason to support your answer.

What is a chemical change?
Give two examples of chemical changes.

Name the class in which:

1. Syrinx is present.
2. Pneumatic bones are present.

Calculate the change in momentum of a body weighing 5kg when its velocity decreases from 20m/s to 0.20m/s.

Water sprinkler used for grass lawns begins to rotate as soon as the water is supplied. Explain the principle on which it works.

Represent graphically by two separate diagrams:

Two sound waves having the same amplitude but different frequencies?

The composition of two atomic particles is given below:

	X	Y
Protons	8	8
Neutrons	8	9
Electrons	8	8

1. What is the mass number of X?
2. What is the mass number of Y?
3. What is the relation between X and Y?
4. Which element/ elements do they represent?

What is meant by ‘reflection of sound’? What type of surface are the best reflecting sound?

What type of thickening of cell wall does occur in collenchymas?