CBSE Class 11 Physics Chapter 2 Notes: Motion in a Straight Line - FREE PDF Download
FAQs on Motion in a Straight Line Class 11 Notes: CBSE Physics Chapter 2
1. What is the core difference between distance and displacement for an object in motion?
The core difference lies in their definitions. Distance is a scalar quantity representing the total path length covered. In contrast, displacement is a vector quantity representing the shortest straight-line path between the initial and final points. For a quick revision, remember displacement can be zero (if the object returns to its start), while distance cannot (unless no motion occurs).
2. When revising, what is the key distinction between speed and velocity?
The key distinction is that speed is a scalar quantity that tells you how fast an object is moving (magnitude only), while velocity is a vector quantity that describes both how fast it is moving and in which direction. An object can have a constant speed but a changing velocity if its direction of motion changes.
3. What defines uniformly accelerated motion, and why is it a key concept in this chapter?
Uniformly accelerated motion is defined as motion where the velocity of an object changes by equal amounts in equal intervals of time. In simpler terms, its acceleration is constant. It's a key concept because it describes many real-world scenarios, like an object falling freely under gravity, and allows the use of simple kinematic equations for analysis.
4. How can a position-time (x-t) graph give a complete summary of an object's motion in a straight line?
A position-time (x-t) graph provides a complete visual summary by showing an object's location at any given moment. Key insights for revision include:
- The slope of the graph at any point gives the instantaneous velocity.
- A straight line indicates constant velocity.
- A curved line (parabola) indicates acceleration.
- A horizontal line means the object is at rest.
5. Can an object have zero velocity but still be accelerating? If so, provide a quick example.
Yes, an object can have zero velocity at a specific instant while still accelerating. A classic example is a ball thrown vertically upwards. At the very peak of its trajectory, its instantaneous velocity is zero for a moment before it changes direction, but the acceleration due to gravity is still acting on it downwards.
6. What are the three main kinematic equations for uniform acceleration, and what does each variable represent?
The three main kinematic equations, essential for revision, describe motion with constant acceleration as per the CBSE 2025-26 syllabus:
- v = u + at
- s = ut + ½ at²
- v² = u² + 2as
7. Why is the slope of a velocity-time (v-t) graph significant for revision, and what physical quantity does the area under it represent?
The velocity-time (v-t) graph is significant because its features directly translate to key motion concepts.
- The slope of the v-t graph (change in velocity / change in time) represents the object's acceleration. A constant slope means constant acceleration.
- The area under the v-t graph represents the object's displacement over that time interval.
8. For a quick recap, what is meant by a 'frame of reference' and a 'point mass object' in kinematics?
For a quick recap:
- A frame of reference is a coordinate system or a set of axes used to measure the position and motion of objects. It's the perspective from which motion is observed.
- An object is treated as a point mass object when its size is negligible compared to the distance it travels. This simplifies calculations by ignoring the object's dimensions.
9. If the acceleration of a particle is constant and not zero, what can you conclude about its velocity-time and position-time graphs?
If a particle has constant, non-zero acceleration, you can conclude the following about its motion graphs:
- Its velocity-time (v-t) graph will be a straight line with a non-zero slope. The slope's value is equal to the constant acceleration.
- Its position-time (x-t) graph will be a parabola. The curve opens upwards for positive acceleration and downwards for negative acceleration.
10. What is the concept of relative velocity and how is it calculated for two objects moving in a straight line?
Relative velocity is the velocity of an object with respect to another object (the observer). For two objects, A and B, moving along a straight line with velocities Vₐ and Vₑ:
- The velocity of A relative to B (Vₐₑ) is calculated as Vₐₑ = Vₐ - Vₑ.
- This concept is crucial for understanding that motion can be described differently from different viewpoints.

















