Why Do we Fall Ill — Science STD 9 — Question

Why the symbols of few elements, like sodium, do not start with the initial letter of the name?

Define the terms and given one example: Coelom.

The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?

Name the following:

1. Cavity present in the body of sponges.
2. Cavity present in the body of cnidarians.

A cricket ball is seen to hit the bat first and the sound of hitting is heard a little later. Why?

What is the name of sheath of nerve fibre?

Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?

What is meant by the ‘molar mass’ of a substance? State the unit in which molar mass is usually expressed.

Name three most important nutrients required for plant growth.

What is reverberation? What will happen if the reverberation time in a big hall is too long?