Atoms and Molecules — Science STD 9 — Question

There are two types of forces X and Y. The forces belonging to type X can produce motion in a stationary object but cannot change the shape of the object. On the other hand, forces belonging to type Y cannot produce motion in a stationary object but can change the shape of the object. What is the general name of the forces such as (a) X, and (b) Y?

What is the number of molecules in 1.5 moles of ammonia?

Akhtar, Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum. Comment on these suggestions.

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

What is a molecule? Explain with an example.

Identify animal groups having:

1. Soft bodied animals supported by calcareous shells.
2. Spiny body has radial body symmetry.
3. Bones light and hollow.
4. Four pairs of jointed legs and no wings.
5. Extemal ear or pinna.

Calculate the pressure when a force of 200N is exerted on an area of: (i) 10m² (ii) 5m².

How does perspiration or sweating help keep our body cool on a hot day?

A body floats in kerosene of density 0.8 × 10³ kg/m³ up to a certain mark. If the same body is placed in water of density 1.0 × 10³kg/m³, will it sink more or less? Give reason for your answer.