Most Expected Questions and Answers
Question 1. What is motion?
Answer:
Motion is the change in position of an object with time with respect to a reference point.
For example, a car moving on a road is in motion with respect to a person standing on the roadside.
Question 2. What is a reference point?
Answer:
A reference point is a fixed point used to describe the position or motion of an object.
For example, if we say that a shop is 250 m from home, then home is the reference point.
Question 3. What is rest?
Answer:
An object is said to be at rest if its position does not change with time with respect to a reference point.
For example, a book lying on a table is at rest with respect to the table.
Question 4. What is motion in a straight line?
Answer:
Motion in a straight line is the motion of an object along a straight path. It is also called linear motion.
Examples include a train moving on a straight track and a ball falling vertically downward.
Question 5. Differentiate between distance and displacement.
Answer:
| Distance | Displacement |
|---|---|
| It is the total path covered by an object. | It is the net change in position. |
| It has only magnitude. | It has magnitude and direction. |
| It is a scalar quantity. | It is a vector quantity. |
| It depends on the path followed. | It depends only on initial and final positions. |
| It can never be negative. | It can be positive, negative, or zero. |
Question 6. Can displacement be zero even when distance is not zero? Explain.
Answer:
Yes, displacement can be zero even when distance is not zero.
For example, if a person goes from home to a shop and returns home, the total distance travelled is not zero. But the initial and final positions are the same, so displacement is zero.
Question 7. When are distance and magnitude of displacement equal?
Answer:
Distance and magnitude of displacement are equal when an object moves in a straight line in one direction without turning back.
For example, if a car moves 100 m straight ahead, then distance = 100 m and displacement = 100 m in that direction.
Question 8. Define average speed.
Answer:
Average speed is the total distance travelled divided by the total time taken.
Formula:
Average speed = Total distance travelled / Time interval
Its SI unit is m s⁻¹.
Question 9. Define average velocity.
Answer:
Average velocity is the displacement of an object divided by the time interval.
Formula:
Average velocity = Displacement / Time interval
It has both magnitude and direction.
Question 10. Differentiate between average speed and average velocity.
Answer:
| Average Speed | Average Velocity |
|---|---|
| It is total distance divided by time. | It is displacement divided by time. |
| It is a scalar quantity. | It is a vector quantity. |
| It has no direction. | It has direction. |
| It cannot be negative. | It can be positive, negative, or zero. |
Question 11. A student walks 60 m east and then 40 m west. Find distance and displacement.
Answer:
Distance travelled = 60 m + 40 m = 100 m
Displacement = 60 m east − 40 m west = 20 m east
Therefore, distance = 100 m and displacement = 20 m east.
Question 12. A car travels 150 km in 3 hours. Find its average speed.
Answer:
Average speed = Total distance / Time
Average speed = 150 km / 3 h = 50 km h⁻¹
Therefore, the average speed of the car is 50 km h⁻¹.
Question 13. A boy runs around a circular track and returns to the starting point. What is his displacement?
Answer:
His displacement is zero because his initial and final positions are the same.
However, the distance travelled is not zero because he has covered the path around the track.
Question 14. Define acceleration.
Answer:
Acceleration is the rate of change of velocity with time.
Formula:
Acceleration = Change in velocity / Time interval
SI unit = m s⁻²
Question 15. What does negative acceleration mean?
Answer:
Negative acceleration means that acceleration is opposite to the direction of velocity.
It usually happens when an object slows down.
Example: A car slows down after brakes are applied.
Question 16. Can an object have zero acceleration but non-zero velocity?
Answer:
Yes, an object can have zero acceleration but non-zero velocity.
For example, a car moving with constant velocity on a straight road has zero acceleration, but its velocity is not zero.
Question 17. A car changes its velocity from 10 m s⁻¹ to 30 m s⁻¹ in 5 s. Find acceleration.
Answer:
Given:
u = 10 m s⁻¹
v = 30 m s⁻¹
t = 5 s
Acceleration = (v − u) / t
= (30 − 10) / 5
= 20 / 5
= 4 m s⁻²
Question 18. What does a position-time graph represent?
Answer:
A position-time graph represents the change in position of an object with time.
In this graph, time is taken on the x-axis and position is taken on the y-axis.
Question 19. What does the slope of a position-time graph give?
Answer:
The slope of a position-time graph gives the velocity of the object.
A steeper slope means higher velocity, and a horizontal line means zero velocity.
Question 20. What does a velocity-time graph represent?
Answer:
A velocity-time graph represents the change in velocity of an object with time.
In this graph, time is taken on the x-axis and velocity is taken on the y-axis.
Question 21. What does the slope of a velocity-time graph give?
Answer:
The slope of a velocity-time graph gives acceleration.
If the slope is positive, acceleration is positive. If the slope is negative, acceleration is negative.
Question 22. What does the area under a velocity-time graph give?
Answer:
The area under a velocity-time graph gives displacement.
For example, if a car moves with constant velocity, displacement = velocity × time.
Question 23. What kind of motion is represented by a straight line position-time graph?
Answer:
A straight line position-time graph represents motion with constant velocity.
This means the object covers equal displacements in equal intervals of time.
Question 24. What kind of motion is represented by a curved position-time graph?
Answer:
A curved position-time graph represents motion with changing velocity.
This means the object is undergoing accelerated motion.
Question 25. Write the three kinematic equations for constant acceleration.
Answer:
The three kinematic equations are:
- v = u + at
- s = ut + ½at²
- v² = u² + 2as
Here,
u = initial velocity,
v = final velocity,
a = acceleration,
t = time,
s = displacement.
Question 26. A car starts from rest and accelerates at 2 m s⁻² for 5 s. Find its final velocity.
Answer:
Given:
u = 0 m s⁻¹
a = 2 m s⁻²
t = 5 s
Using:
v = u + at
v = 0 + 2 × 5
v = 10 m s⁻¹
Therefore, final velocity is 10 m s⁻¹.
Question 27. A car starts from rest and accelerates at 2 m s⁻² for 5 s. Find the distance travelled.
Answer:
Given:
u = 0 m s⁻¹
a = 2 m s⁻²
t = 5 s
Using:
s = ut + ½at²
s = 0 × 5 + ½ × 2 × 5²
s = 25 m
Therefore, the distance travelled is 25 m.
Question 28. What is uniform circular motion?
Answer:
When an object moves in a circular path with constant speed, its motion is called uniform circular motion.
Example: The tip of a clock hand moving in a circular path.
Question 29. Why is uniform circular motion called accelerated motion?
Answer:
Uniform circular motion is called accelerated motion because the direction of velocity changes continuously.
Even though speed remains constant, velocity changes because velocity has direction.
Question 30. What is the displacement of an object after one complete revolution in a circular path?
Answer:
The displacement after one complete revolution is zero.
This is because the object returns to its starting point after completing one full circle.
15 Short Question Answers
Question 1. What is meant by motion?
Answer:
Motion is the change in position of an object with time with respect to a reference point. For example, a car moving on a road is in motion with respect to a person standing on the roadside.
Question 2. What is a reference point?
Answer:
A reference point is a fixed point used to describe the position of an object. For example, if we say that a shop is 250 m from home, then home is the reference point.
Question 3. Define distance travelled.
Answer:
Distance travelled is the total length of the path covered by an object. It has only magnitude and no direction. It is a scalar quantity and its SI unit is metre.
Question 4. Define displacement.
Answer:
Displacement is the net change in the position of an object between two given instants of time. It has both magnitude and direction, so it is a vector quantity.
Question 5. Write two differences between distance and displacement.
Answer:
Distance is the total path covered by an object, while displacement is the shortest distance between initial and final positions with direction. Distance is a scalar quantity, whereas displacement is a vector quantity.
Question 6. When are distance and magnitude of displacement equal?
Answer:
Distance and magnitude of displacement are equal when an object moves in a straight line in one direction without turning back. For example, if a car moves 100 m straight ahead, its distance and displacement magnitude are both 100 m.
Question 7. Define average speed.
Answer:
Average speed is the total distance travelled divided by the total time taken.
Average speed = Total distance travelled / Time interval
Its SI unit is m s⁻¹.
Question 8. Define average velocity.
Answer:
Average velocity is the displacement of an object divided by the time interval.
Average velocity = Displacement / Time interval
It has both magnitude and direction.
Question 9. Define acceleration.
Answer:
Acceleration is the rate of change of velocity with time.
Acceleration = Change in velocity / Time interval
Its SI unit is m s⁻².
Question 10. What does negative acceleration mean?
Answer:
Negative acceleration means acceleration is opposite to the direction of velocity. It usually happens when an object slows down, such as a car after brakes are applied.
Question 11. What does a position-time graph represent?
Answer:
A position-time graph represents how the position of an object changes with time. In this graph, time is taken on the x-axis and position is taken on the y-axis.
Question 12. What does the slope of a position-time graph give?
Answer:
The slope of a position-time graph gives the velocity of the object. A steeper slope shows greater velocity, while a horizontal line shows zero velocity.
Question 13. What does the slope of a velocity-time graph give?
Answer:
The slope of a velocity-time graph gives acceleration. A positive slope shows increasing velocity, while a negative slope shows decreasing velocity.
Question 14. What does the area under a velocity-time graph give?
Answer:
The area under a velocity-time graph gives displacement. For example, for constant velocity, displacement = velocity × time.
Question 15. What is uniform circular motion?
Answer:
When an object moves in a circular path with constant speed, its motion is called uniform circular motion. In this motion, speed remains constant, but velocity changes because direction changes continuously.
10 Long Question Answers
Question 1. Explain the difference between distance and displacement with an example.
Answer:
Distance and displacement are both used to describe motion, but they are different quantities.
Distance is the total length of the path covered by an object. It does not have any direction. It is a scalar quantity. Distance depends on the actual path followed by the object.
Displacement is the net change in the position of an object. It is the shortest distance between the initial and final positions, along with direction. It is a vector quantity.
For example, suppose a person walks 100 m east and then 60 m west.
Total distance travelled = 100 m + 60 m = 160 m
Displacement = 100 m east − 60 m west = 40 m east
Thus, distance is 160 m, but displacement is 40 m east.
Distance can never be negative, while displacement can be positive, negative, or zero depending on direction. If an object returns to its starting point, displacement becomes zero, but distance travelled is not zero.
Question 2. Explain average speed and average velocity with an example.
Answer:
Average speed and average velocity describe how fast an object moves, but they are not the same.
Average speed is the total distance travelled divided by the total time taken.
Average speed = Total distance travelled / Time interval
It is a scalar quantity because it has only magnitude and no direction.
Average velocity is the displacement divided by the time interval.
Average velocity = Displacement / Time interval
It is a vector quantity because it has both magnitude and direction.
Example: A person walks 200 m north in 3 minutes and then 200 m south in 2 minutes.
Total distance = 200 m + 200 m = 400 m
Total time = 3 min + 2 min = 5 min
Average speed = 400 / 5 = 80 m/min
Since the person returns to the starting point, displacement = 0 m.
Average velocity = 0 / 5 = 0 m/min
Thus, average speed is 80 m/min, but average velocity is 0 m/min.
Question 3. What is acceleration? Explain positive and negative acceleration.
Answer:
Acceleration is the rate of change of velocity with time. It tells us how quickly the velocity of an object changes.
Acceleration = Change in velocity / Time interval
If the initial velocity is u, final velocity is v, and time taken is t, then:
a = (v − u) / t
The SI unit of acceleration is m s⁻².
Acceleration can be positive, negative, or zero.
Positive acceleration occurs when the velocity of an object increases with time. For example, when a car starts from rest and speeds up, it has positive acceleration.
Negative acceleration occurs when the velocity of an object decreases with time. It is also called retardation or deceleration. For example, when brakes are applied to a moving car, its velocity decreases and acceleration acts opposite to the direction of motion.
If an object moves with constant velocity in a straight line, its acceleration is zero because its velocity does not change.
Question 4. Explain position-time graph and its different shapes.
Answer:
A position-time graph shows how the position of an object changes with time. In this graph, time is usually taken on the x-axis and position is taken on the y-axis.
The shape of a position-time graph tells us about the nature of motion.
A straight line position-time graph shows uniform motion. It means the object covers equal displacements in equal intervals of time. Therefore, the object has constant velocity.
A curved position-time graph shows non-uniform motion. It means the velocity of the object is changing with time. Therefore, the object is in accelerated motion.
A horizontal position-time graph shows that the object is at rest. This is because its position does not change with time.
The slope of a position-time graph gives velocity.
If the slope is steep, velocity is high. If the slope is less steep, velocity is low. If the slope is zero, velocity is zero.
Question 5. Explain velocity-time graph and the quantities obtained from it.
Answer:
A velocity-time graph shows how the velocity of an object changes with time. In this graph, time is taken on the x-axis and velocity is taken on the y-axis.
The shape of a velocity-time graph tells us about the nature of motion.
A horizontal velocity-time graph shows constant velocity. In this case, acceleration is zero.
A straight line sloping upward shows that velocity is increasing uniformly. This means the object has constant positive acceleration.
A straight line sloping downward shows that velocity is decreasing uniformly. This means the object has negative acceleration or retardation.
Two important quantities can be obtained from a velocity-time graph:
First, the slope of the graph gives acceleration.
Acceleration = Change in velocity / Change in time
Second, the area under the velocity-time graph gives displacement.
For example, if a car moves with velocity 20 m/s for 5 s, then displacement = area under graph = 20 × 5 = 100 m.
Thus, velocity-time graphs help us find both acceleration and displacement.
Question 6. Write and explain the three kinematic equations for uniformly accelerated motion.
Answer:
Kinematic equations describe the motion of an object moving in a straight line with constant acceleration.
There are five quantities involved:
u = initial velocity
v = final velocity
a = acceleration
t = time
s = displacement
The three kinematic equations are:
First equation:
v = u + at
This equation is used to find final velocity when initial velocity, acceleration, and time are known.
Second equation:
s = ut + ½at²
This equation is used to find displacement when initial velocity, acceleration, and time are known.
Third equation:
v² = u² + 2as
This equation is used when time is not given or not required.
These equations are valid only when acceleration is constant. They are very useful for solving problems related to vehicles, falling objects, and motion in a straight line.
Question 7. A car starts from rest and reaches a velocity of 20 m/s in 5 s. Find acceleration and distance travelled.
Answer:
Given:
Initial velocity, u = 0 m/s
Final velocity, v = 20 m/s
Time, t = 5 s
Acceleration:
a = (v − u) / t
a = (20 − 0) / 5
a = 4 m/s²
Now, distance travelled:
s = ut + ½at²
s = 0 × 5 + ½ × 4 × 5²
s = 2 × 25
s = 50 m
Therefore:
Acceleration = 4 m/s²
Distance travelled = 50 m
Question 8. Why is uniform circular motion called accelerated motion?
Answer:
Uniform circular motion is the motion of an object in a circular path with constant speed.
In this motion, the speed of the object remains constant, but the direction of motion changes continuously. Since velocity depends on both speed and direction, the velocity of the object keeps changing at every point on the circular path.
Acceleration is defined as the rate of change of velocity. Therefore, even though speed is constant, the object is accelerating because its velocity is changing due to continuous change in direction.
For example, a stone tied to a string and whirled in a circle moves with constant speed, but its direction changes continuously. Hence, it is in accelerated motion.
Thus, uniform circular motion is accelerated motion because the direction of velocity changes continuously.
Question 9. Explain rest and motion as relative terms.
Answer:
Rest and motion are relative terms because they depend on the reference point chosen.
An object may be at rest with respect to one reference point but in motion with respect to another reference point.
For example, a student sitting inside a moving bus is at rest with respect to other passengers in the bus because his position does not change with respect to them. However, the same student is in motion with respect to a person standing on the road because his position changes with respect to that person.
Similarly, an object kept on Earth is at rest with respect to Earth. But it is in motion with respect to the Sun because Earth moves around the Sun.
Therefore, whether an object is at rest or in motion depends on the reference point.
Question 10. Explain why it is important to maintain a safe distance from a vehicle moving ahead.
Answer:
It is important to maintain a safe distance from a vehicle moving ahead because a moving vehicle cannot stop immediately when brakes are applied.
When the driver sees an obstacle or another vehicle suddenly stopping, the driver first takes some time to react. During this reaction time, the vehicle continues to move forward. After the brakes are applied, the vehicle still covers some distance before coming to rest. This distance is called stopping distance.
Stopping distance depends on several factors, such as:
Speed of the vehicle
Condition of brakes
Condition of road
Driver’s reaction time
Mass of the vehicle
Condition of tyres
If the speed is higher, the stopping distance is also greater. Therefore, when we drive fast, we should maintain a larger safe distance from the vehicle ahead.
Maintaining safe distance helps avoid collisions and makes road travel safer.
