Improvement in Food Resources — Science STD 9 — Question

Why is heat energy needed to melt a solid? What is this heat energy called?

A body is moving uniformly in a straight line with a velocity of 5m/s. Find graphically the distance covered by it in 5 seconds.

Why are leguminous crops desirable in crop rotation?

A ball falls to the ground as shown below:

1. ♦ Potential energy = 80 J, Kinetic energy = 0
2. ♦ Kinetic energy = 48J
3. ♦ Potential energy = 0

1. What is the kinetic energy of ball when it hits the ground?
2. What is the potential energy of ball at B?
3. Which law you have made use of in answering this this question?

When do we say that work is done? Write the formula for the work done by a body in moving up against gravity. Give the meaning of each symbol which occurs in it.

Explain by an example what is meant by potential energy. Write down the expression for gravitational potential energy of a body of mass m placed at a height h above the surface of the earth.

Explain various steps in hybridization of crop plants.

How much electric energy in kWh is consumed by an electrical appliance of 1000 watts when it is switched on for 60 minutes?

The scientists now say that there are actually five states of matter A, B, C, D and E. The state A has a fixed volume but no fixed shape. The state B can be compressed very easily by applying pressure and state C has a fixed shape as well as a fixed volume. The state D is mixture of free electrons and ions whereas state E is named after an Indian scientist and a famous physicist.

1. Name the physical states (i) A (ii) B (iii) C (iv) D, and (v) E.
2. Name one substance belonging to state C which can directly change into vapours on heating. What is this process known as?
3. Name one substance which normally belongs to state B but whose solid form changes directly into gaseous state.
4. Name the most common substance belonging to state A.
5. Which state of matter makes the sum and other stars to glow.