Structure of the Atom — Science STD 9 — Question

Giving reasons state the reading on a spring balance when it is attached to a floating block of wood which weighs 50g in air.

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

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?

A car is moving on a level road. If the driver turns off the engine of the car, the car’s speed decreases gradually and ultimately it comes to a stop. A student says that two forces act on the car which bring it to a stop. What could these forces be? Which of these two forces contributes more to slow down and stop the car?

If the mass of a body and the force acting on it are both doubled, hat happens to the acceleration?

How does the water kept in an earthen pot (matka) become cool during summer?

What are fertilizers? Classify fertilizers.

Which of the following are chemical changes?

1. Growth of a plant.
2. Rusting of iron.
3. Mixing of iron filings and sand.
4. Cooking of food.
5. Digestion of food.
6. Freezing of water.
7. Burning of a candle.

Explain why, diffusion occurs more quickly in a gas than in al iquid.