Sound — Science STD 9 — Question

In which type of change a new substance is formed?

When is a body said to have uniform velocity?

Does density vary with temperature?

Five electric fans of 120 watts each are used for 4 hours. Calculate the electrical energy consumed in kilowatt hours.

What are tracheary elements? Describe their functions.

An object is moving along a straight line with uniform acceleration. The following table gives the velocity of the object at various instants of time:

Time (in sec.):	0	1	2	3	4	5	6
Velocity (in m/s):	2	4	6	8	10	12	14

Plot the graph.
From the graph,

1. Find the velocity of the object at the end of 2.5 seconds.
2. Calculate the acceleration.
3. Calculate the distance covered in the last 4 seconds.

Why don't we really see moon falling towards the earth?

Two different bodies are completely immersed in water and undergo the same loss in weight. Is it necessary that their weights in air should also be the same? Explain.

Two persons manage to push a motorcar of mass 1200kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2m s^-2. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)

State an important characteristic of uniform circular motion. Name the force which brings about uniform circular motion.