PHYSICS Ch 1

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 center 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 covered 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.

Question 16.

Does the speedometer of a car measure its average speed?

Answer:

No. It measures its instantaneous speed.

Question 17.

A body is moving with a velocity of 10 m/s. If the motion is uniform, what will be the velocity after 10 s?

Answer:

As the motion is uniform, the velocity remains 10 m/s after 10 s.

Question 18.

Can a body have constant speed but variable velocity?

Answer:

Yes, e.g. a body in uniform circular motion has constant speed but due to the change in the direction of motion, its velocity changes at every point.

Question 19.

When is the acceleration taken as negative?

Answer:

Acceleration is taken as negative if it is in the direction opposite to the direction of velocity.

Question 20.

What is uniform acceleration?

Answer:

Acceleration of an object is said to be uniform if it travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time. For example, motion of a freely falling body.