Give reasons:
1. A body cannot exist at a state of absolute rest or absolute motion.
2. The weight of an object is not a constant quantity.
3. While travelling in a train, it appears that the trees near the track are moving whereas co-passengers appear
to be stationary
IV. Answer the following:
1. Differentiate between attractive and directive property of a magnet. 2. A bar magnet has no markings to indicate its poles. How would you find out its North pole? 3. A boy burst a balloon. The other boy hears the sound after 0.6 seconds. If the speed of sound is 332 m/s, find
the distance between the two boys .
4. Two astronauts were floating close to each other in space. Can they talk to each other without using any special
device? Give reasons.
5. Vimal bought a powerful music system capable of playing loud music. He placed it on a table and kept rice
grains on its speaker. After sometime of playing the music, the rice grains fell off the speaker. Why do
you think it happened?
6. We have a stringed musical instrument. The string is plucked in the middle first with the force of greater
magnitude and then with a force of smaller magnitude, In which case would the instrument produce a louder
sound?
Answers
Answer:
1. It is because our body possesses energy to do work . When we have energy , we are capable of doing work and remain in motion and when our energy is used up , our body comes in a state of rest .
2. It is because the weight of the body varies from place to place . For eg. , our weight on moon is one sixth of the weight on earth.
3. It is because the train is in motion , so it seems as if the trees are also in motion while the co - passengers are at rest , so they appear to be at rest .
IV.
1.• Attractive property:
A magnet attracts magnetic substances towards itself. This property of a magnet is called its attractive property.
• Directive property:
a freely suspended magnet always rests in the north south direction. This property of the magnet is called its directive property.
2. We can find out its North pole by :
a. Suspend your bar magnet on a stand .
b. The north seeking pole of the Earth is the north pole while the south seeking pole of the Earth is the South pole .
c. NOTE : A freely suspended bar magnet always lies in the north-south direction.
3. Speed of sound = Distance travelled ÷ Time taken
Therefore,
332 =d÷0.6
d = 332 × 0.6 = 199.2m
4. No they cannot talk to each other in space without using any special device . It is because sound always needs a medium to propagate but in space there is no medium but vacuum. So the sound cannot propagate and the astronauts cannot talk to each other.
5. It happened because the speaker converts the electrical energy into sound energy and due to which vibrations are produced . Hence , the vibrations produced cause the solid particles to vibrate about their fixed position. Due to this vibration , the rice grains fall off the speaker .
6. The loudness of sound depends on the amplitude of vibration. therefore the instrument will produce a sound when it is strucked with a greater force of magnitude.
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