4. Lalit while watching ‘National Geographic’ channel on television observed that Bats
could easily fly during the night. He did not understand the concept and for this he
surfed on internet, and finally found the answer that bats use ultrasonic sound
waves to fly and search their prey at night.
a) What are ultrasonic sound waves? State its one application.
b) Differentiate between ultrasonic and infrasonic sound waves.
5. Sumit is a student of class IX. He was waiting for a bus at the bus stand. He saw an
old man trying hard to keep his luggage over the roof of a bus. Sumit picked up his
luggage and placed the luggage over the roof of the bus. The old man thanked Sumit.
Answer the following questions based on the above paragraph.
a) Is the work done by Sumit while placing the luggage on the roof of the bus positive
or negative?
b) What will be the direction of work done by gravity with respect to luggage?
6. Two particles are placed at some distance. If the mass of each of the two particles is
doubled, and the distance between them is reduced to half, what will happen to the
value of gravitational force between them?
7. An object of mass 100 kg is accelerated uniformly from a velocity of 5 m s−1 to 8
ms−1 in 6 s. Calculate the initial and final momentum of the object. Also, find the
magnitude of the force exerted on the object.
CHEMISTRY
1. A student was determining the melting point of ice in the laboratory. The teacher
was taking the round. He found that the student was not using any stirrer. Teacher
asked him to use a glass stirrer and then determine the melting point of ice.
a) Is the use of a stirrer necessary during heating?
b) What is its purpose?
2. The difference between mass of 100 moles of sodium atoms and sodium ions is
5.48002g.
a) Compute the mass of an electron.
b) State the difference between a sodium atom and sodium ion.
3. A student was asked by his teacher to separate an impure sample of sulphur
containing sand as the impurity. He tried to purify it with the help of sublimation.
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