Motion Class 9 Worksheet Science Chapter 7

Q.1. Fill in the blanks

(i) _______ and _______ are used to describe the overall motion of an object and to locate its final position with reference to its initial position at a given time.
Ans: distance, displacement

Distance and displacement are physical quantities used to describe how far an object has traveled and its final position relative to its starting point. Distance is the total path length covered, while displacement is the shortest straight-line distance from the initial to the final position.

(ii) An object is said to be in ________ if it changes its position with respect to its surroundings in a given time.
Ans: motion

An object is said to be in motion when it changes its position relative to a reference point over time, indicating movement.

(iii) The quantity that specifies both the speed and the _______ of an object’s motion is called velocity.

Ans: direction

Velocity is defined as the speed of an object in a specific direction, making it a vector quantity that includes both magnitude and direction.

(iv) The distance time graph for __________ is a straight line.

Ans: Uniform motion

Uniform motion refers to motion at a constant speed in a straight line, represented graphically as a straight line on a distance-time graph.

(v) A non uniform motion is also called an __________ motion.

Ans: accelerated

A non-uniform motion is also referred to as accelerated motion, where the velocity of the object changes over time, indicating varying speeds.

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.

For example, if an object moves 10 metres forward and then 10 metres back, its displacement is zero, even though it has travelled a total distance of 20 metres.

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 can have a constant acceleration while having a zero velocity. For example:

• A ball dropped from rest at a height experiences a gravitational acceleration of 9.81 m/s² towards the Earth, even though its initial velocity is zero.

(b) An object can move in a specific direction while experiencing acceleration in a perpendicular direction. For instance:

• An athlete running along a circular path maintains a constant speed, but the direction of their velocity changes constantly. The acceleration is directed towards the centre of the circle, which is perpendicular to their motion.

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 calculate 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

Given:

• Initial velocity (u) = 0
• Acceleration (a) = 0.2 m/s²
• Time (t) = 300 seconds

Calculating the final speed:

• v = 0 + (0.2 × 300) = 60 m/s

Now, calculating the distance travelled:

• S = 0 + ½ × 0.2 × (300)²
• S = 0 + 0.1 × 90000 = 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, which means the object is accelerated. This acceleration occurs even though the speed remains constant. The force that causes this type of motion is known as centripetal force.