class 9 ch 8 science extra questions.
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Answers
Answer:
Question 1.
The phenomenon of motion was placed on a sound scientific footing by two scientists. Write their names.
Answer:
Galileo Galilei and Isaac Newton.
Question 2.
Are rest and motion absolute or relative terms?
Answer:
They are relative terms.
Question 3.
Suppose a ball is thrown vertically upwards from a position P above the ground. It rises to the highest point Q and returns to the same point P. What is the net displacement and distance travelled by the ball?
Answer:
Displacement is zero. Distance is twice the distance between position P and Q.
Question 4.
Which speed is greater: 30 m/s or 30 km/h?
Answer:
30 m/s
Question 5.
What do you mean by 2 m/s2?
Answer:
The velocity of the body increases by 2 m/s after every second.
Question 6.
Can uniform linear motion be accelerated?
Answer:
No
Question 7.
Define one radian.
Answer:
It is the angle which is subtended at the centre by an arc having a length equal to the radius of the circle.
Question 8.
What is the relation between linear velocity and angular velocity?
Answer:
Linear velocity = Angular velocity × Radius of circular path.
Question 9.
Give an example when we infer the motion indirectly.
Answer:
We infer the motion of air by observing the movement of dust particles or leaves and branches of trees, or simply by feeling the blowing air on our face.
Question 10.
What is essential to describe the position of an object?
Answer:
We need to specify a reference point called the origin.
Question 11.
What is the simplest type of motion?
Answer:
Motion in a straight line.
Question 12.
What indicates the motion of the earth?
Answer:
The phenomenon like day and night indicates the motion of the earth.
Question 13.
If the displacement of a body is zero, is it necessary that the distance coyered by it is also zero?
Answer:
No. When the body comes back to the same position after travelling a distance, its displacement is zero though it has travelled some distance.
Question 14.
Can the displacement be greater than the distance travelled by an object?
Answer:
No, it is always either equal to or less than the distance travelled by the object.
Question 15.
When do the distance and displacement of a moving object have the same magnitude?
Answer:
The magnitude of distance and displacement of a moving object are same when the object moves along the same straight line in the same fixed direction.