Motion Class 9 Worksheet Science Chapter 7

Q.1. Fill in the blanks:

(i) The branch of Physics, which deals with the behaviour of moving objects, is known as Mechanics.
(ii) An object is said to be in motiom if it changes its position with respect to its surroundings in a given time.
(iii) A Frame of reference is another object of scene with respect to which we compare an object's position.
(iv) The distance time graph for Uniform motion is a straight line.
(v) A non uniform motion is also called an accelerated motion.

Q.2. The numerical ratio of displacement to distance for a moving object is: 
(a) Always less than 1
(b) Equal to 1 or more than 1
(c) Always more than 1
(d) Equal to 1 or less than 1

Ans. Option (d)

The numerical ratio of displacement to distance for a moving object can be described as follows:

• It can be equal to 1 when the path taken is straight.
• It can be less than 1 if the object moves in a curved path.

Thus, the ratio is always equal to 1 or less than 1.

Q.3. A boy is sitting on a merry-go-round which is moving with a constant speed of 10 m S–1. This means that the boy is:
(a) At rest
(b) Moving with no acceleration
(c) In accelerated motion
(d) Moving with uniform velocity

Ans. Option (c)

• The boy is in accelerated motion while sitting on the merry-go-round.
• Even though he moves at a constant speed of 10 m/s, the direction of his motion changes continuously.
• This change in direction means he is experiencing centripetal acceleration.

Q.4. In which of the following cases of motion, the distance moved and the magnitude of displacement are equal ? 
(a) If the car is moving on straight road
(b) If the car is moving on circular road
(c) If the pendulum is moving to and fro
(d) If a planet is moving around the sun

Ans. Option (a)

The distance moved and the magnitude of displacement are equal when the car is moving on a straight road.

For other options:

• On a circular road, the distance is greater than the displacement.
• A pendulum moving to and fro covers more distance than its displacement.
• A planet moving around the sun also has a greater distance than its displacement.

Q.5. The speed of a moving object is determined to be 0.06 m/s. this speed is equal to:
(a) 2.16 km/h
(b) 1.08 km/h
(c) 0.216 km/h
(d) 0.0216 km/h

Ans. Option (c)

The speed of the moving object is 0.06 m/s. To convert this speed into kilometres per hour (km/h), we use the following conversion:

• 1 m/s is equivalent to 3.6 km/h.
• Therefore, to convert 0.06 m/s to km/h:
• 0.06 m/s × 3.6 = 0.216 km/h.

Thus, the correct answer is option (c) 0.216 km/h.

Q.6. Is displacement a scalar quantity?
Ans. 

• Displacement is a vector quantity, meaning it has both magnitude and direction. Its units include metres and kilometres.
• In contrast, a scalar quantity only has magnitude and no direction. Examples of scalar quantities include distance and speed.
• Thus, displacement differs from distance, as it considers the shortest path between two points.

Q.7. State whether distance is a scalar or a vector quantity.
Ans. Distance is a scalar quantity. It is measured in units such as:

• Metres
• Kilometres

Unlike vector quantities, distance does not require a direction to be specified. It only needs a numerical value.

Q.8. Give one example of a situation in which a body has a certain average speed but its average velocity is zero.
Ans: Movement around a circular track is an example where a body has an average speed but its average velocity is zero.

• When an object moves in a circular path, it returns to its starting point.
• After completing one full round, the displacement is zero.
• Since average velocity depends on displacement, it is also zero.

However, the object can have a non-zero average speed, as it has covered a distance around the track.

Q.9. Which of the two can be zero under certain conditions: average speed of a moving body or average velocity of a moving body?
Ans: Average velocity can be zero under certain conditions. This occurs when:

• The displacement of the body is zero.
• In such cases, the average velocity will also be zero.

In contrast, the average speed of a moving body cannot be zero unless the body is not moving at all.

Q.10. What does the path of an object look like when it is in uniform motion?
Ans: The path of an object in uniform motion is represented graphically as:

• A straight line on a distance-time graph.
• This indicates that the object travels equal distances in equal intervals of time.

Q.11. Distinguish between speed and velocity.
Ans: Speed refers to how fast an object moves, measured as the distance travelled per unit of time. It is a scalar quantity, meaning it only has magnitude and no direction. Velocity, on the other hand, is the speed of an object in a specific direction. It is a vector quantity, which means it includes both magnitude and direction.

• Speed: Distance travelled / Time taken
• Velocity: Displacement / Time taken

Q.12. An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.
Ans: Yes, an object can move through a distance and still have zero displacement. Displacement refers to the change in an object's position from its starting point to its ending point.

• If an object travels from point A to point B and then returns to point A, the total displacement is zero.
• This is because the starting and ending positions are the same, despite the distance travelled being greater than zero.

Q.13. State which of the following situations are possible and give an example for each of these: 
(a) an object with a constant acceleration but with zero velocity 
(b) an object moving in a certain direction with an acceleration in the perpendicular direction.
Ans. (a) An object with a constant acceleration can still have zero velocity. For example, an object which is at rest on the surface of earth will have zero velocity but still be acted upon by the gravitational force of the earth with an acceleration of 9.81 ms^-2 towards the centre of the earth. Hence when an object starts falling freely can have constant acceleration but with zero velocity.
(b) When an athlete moves with a velocity of constant magnitude along the circular path, the only change in his velocity is due to the change in the direction of motion. Here, the motion of the athlete moving along a circular path is, therefore, an example of an accelerated motion where acceleration is always perpendicular to the direction of motion of an object at a given instance. Hence it is possible when an object moves on a circular path.

Q.14. A train starting from rest moves with a uniform acceleration of 0.2 m/s² for 5 minutes. Calculate the speed acquired and the distance travelled in this time.

Ans. The train starts from rest and accelerates uniformly at 0.2 m/s² for 5 minutes (or 300 seconds). To find the speed acquired and the distance travelled, we can use the following equations:

• Final Speed (v): v = u + at
• Distance (S): S = ut + ½ at²

U = 0, v = ?
a = 0.2 m/s²
t = 300 sec
v = 0 + .2 x 300 = 60 m/s
By putting the values in the second equation of motion the distance can be calculated.
S = 0 + ½ × 0.2 × 300 × 300 = 9000 m or 9 km

Q.15. State an important characteristic of uniform circular motion. Name the force which brings about uniform circular motion.
Ans: An important characteristic of uniform circular motion is that the direction of motion changes continuously over time, indicating that it is accelerated. The force responsible for this type of motion is called centripetal force.