Tissues — Science STD 9 — Question

Give reason for the following observations.
Naphthalene balls disappear with time without leaving any solid.

The hanging bob of a simple pendulum is displaced to one extreme position B and then released. It swings towards centre position A and then to the other position C. In which position does the bob have:

1. Maximum potential energy?
2. Maximum kinetic energy?

Give reasons for your answer.

Differentiate the following activities on the basis of voluntary (V) or involuntary (IV) muscles.
Writing with hand.

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

A car falls off a ledge and drops to the ground in 0.5 seconds.
Let g = 10ms^-2, then
What is its speed on striking the ground?

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

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

Give an example of situation in which distance- is equal to displacement.

Which part of the Dalton’s atomic theory came from the law of constant proportions given by Proust?