Atoms and Molecules — Science STD 9 — Question

What is the work done against gravity when a body is moved horizontally along a frictionless surface?

Is the uniform circular motion accelerated? Give reasons for your answer.

Suppose a ball of mass m is thrown vertically upward with an initial speed v, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of initial and final momentums of the ball are same. Yet, it is not an example of conservation of momentum. Explain why?

Name two solid, two liquids and two gaseous elements at the room temperature.

Do action and reaction act on the same body or different bodies? How are they related in magnitude and direction? Are they simultaneous or not?

What is active transport?

Define ‘molecular mass’ of a substance.

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work'.

• Suma is swimming in a pond.
• A donkey is carrying a load on its back.
• A wind mill is lifting water from a well.
• A green plant is carrying out photosynthesis.
• An engine is pulling a train.
• Food grains are getting dried in the sun.
• A sailboat is moving due to wind energy.