Tissues — Science STD 9 — Question

If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and then floats. Why?

In which one of the following cases will the distance covered and the magnitude of the displacement are not the same? Justify.

1. A passenger in a train travels from Delhi to Kolkata.
2. A raindrop falling in still air.
3. An athlete completes one lap in a race.

Which of the following are physical changes and which are chemical changes?

1. Burning of a magnesium wire.
2. Freezing of water.
3. Rusting of iron.
4. Glowing of an electric bulb.

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

An object weighs 10 N when measured on the surface of the earth. What would be its weight when measured on the surface of the moon?

Why is a liquid (the hydraulic fluid) used to operate the brakes in a car?

What type of organization is found in the plasma membrane?

Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures:
Two volatile components with appreciable difference in boiling points.

If 6g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.