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Motion in a Straight Line Class 11 Notes CBSE Physics Chapter 2 (Free PDF Download)

Last updated date: 13th Sep 2024
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Revision Notes for CBSE Class 11 Physics Chapter 2 (Motion in a Straight Line) - Free PDF Download

Just like any other subject, Physics requires continuous practice until you get it right. Class 11 Physics always seems difficult to students due to complex terms, equations and laws present in various crucial chapters of Physics.  It is very important for us to know the basic formulas and to solve questions regularly to understand the topics properly. Class 11 Physics Chapter 2 Motion in a straight line is an important topic as every year many questions come from this chapter in board exams.

Thus, the goal of CBSE class 11 physics notes chapter 2 motion in a straight line is to provide detailed step by step information about the topic in a very easy and understandable manner. It also provides short and readable notes to help students quickly remember the core points before the exam.

Also, check CBSE Class 11 Physics revision notes for other chapters:

Motion In A Straight Line Chapter-Related Important Study Materials
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Motion in a Straight Line Class 11 Notes Physics - Basic Subjective Questions

Section – A (1 Mark Questions)

1. Define the speed of the object.

Ans. The speed of an object is defined as the distance covered by it per unit of time.

2. Can there be motion in two dimensions with acceleration in only one dimension?

Ans. Yes, projectile motion.

3. Is it true that a body is always at rest in a frame that is fixed to the body itself?

Ans. Yes, because the velocity of the body with respect to frame of reference is zero.

4. Tell under what condition a body moving with uniform velocity can be in equilibrium?

Ans. When the net force on the body is zero.

5. What is common between the two graphs shown in figs. (a) and (b)?

Ans. Both these graphs represent that velocity is positive.

Section – B (2 Marks Questions)

6. Can the speed of a body change if its velocity is constant? Why?

Ans. No, the speed of a body cannot change if its velocity is constant which means that both the magnitude and direction of velocity do not change. The magnitude of velocity is speed, so speed cannot change.

7. Is the following graph possible for the motion of a particle moving along a straight line? Explain.

Ans. No.

This is because the speed for a given time is negative and speed is always positive.

8. Draw the position-time and velocity-time graph for a body projected vertically upwards with initial velocity u. Take the projection point to be origin and upward direction as positive.

Ans.

9.A particle moves along a semicircular path of radius R in time t with constant speed. For the particle calculate

(i) distance traveled,

(ii) displacement,

(iii) average speed,

(iv) average velocity,

Ans. (i) Distance = length of path of particle $=AB=\pi R$

(ii) Displacement = minimum distance between initial and final point $=AB=2R$

(iii) Average speed, $V=\dfrac{total\;distance}{time}=\dfrac{\pi R}{t}$

(iv) Average velocity $=\dfrac{2R}{t}$

10. A car travels first half the distance between two places with a speed of 30km/h and the remaining half with a speed of 50km/h. Find the average speed of the car.

Ans. $V_{avg}=\dfrac{S}{t_{1}+t_{2}}=\dfrac{S}{\dfrac{S}{2\times 30}+\dfrac{S}{2\times 50}}=\dfrac{S}{\dfrac{S}{20}\left ( \dfrac{5+3}{15} \right )}$

$V_{avg}=\dfrac{20\times 15}{8}=\dfrac{5\times 15}{2}=\dfrac{75}{2}=37\cdot 5km/h$

PDF Summary - Class 11 Physics Motion in a Straight Line Notes (Chapter 2)

1. Mechanics:

Mechanics refers to the branch of Physics, which involves the study of the movement of physical objects.

It may be broadly categorized into the following branches:

1.1 Statics:

It is the branch of mechanics, which involves the study of physical objects at rest.

1.2 Kinematics:

It is the branch of mechanics, which involves the study of the movement of physical objects without considering the factors that cause movement.

1.3 Dynamics:

It is the branch of mechanics, which involves the study of movement of physical objects considering the factors that cause movement.

2. Rest And Motion

2.1 Rest:

• An object is said to be at rest when it does not change its position with respect to its surroundings.

• For example, the white board in a classroom is at rest with respect to the classroom.

2.2 Motion:

• An object is said to be in motion when it changes its position with respect to its surroundings.

• For instance, when we walk, run or ride a bike, we are said to be in motion with respect to the ground.

2.3 Rest and Motion are Relative:

• Rest and motion are dependent on the observer. The object in one situation may be at rest while the same object in another situation may be in motion.

• For example, the driver of a moving car is in motion with respect to an observer standing on the ground whereas, the same driver is at rest with respect to the man(observer) in the passenger’s seat.

3. While Studying This Chapter:

• We would consider the objects as point mass objects.

• An object can be taken as a point mass object if during the course of motion, it covers distances much greater than its own size.

• We may confine ourselves to the study of rectilinear motion, which is the study of motion of objects along a straight line.

4. Position, Distance, Displacement:

4.1 Position:

• Position of an object is always expressed with respect to some reference point which we generally account to as origin.

• To express the change in position, we consider two physical quantities.

4.2 Distance:

• It refers to the actual path traversed by the object during the course of motion.

• Its S.I. unit is $\text{ }\!\!'\!\!\text{ }m'$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{0}}]$.

4.3 Displacement:

• It refers to the difference between the final and initial positions of the object during the course of motion.

• Its S.I unit is 'm' and its dimensions are M0L1T0.

Differences Between Distance and Displacement:

 Distance Displacement It refers to the actual path traversed by the object during the course of motion. It refers to the difference between the initial and the final positions $\Delta x={{x}_{2}}-{{x}_{1}}$, where, ${{x}_{2}}$ and ${{x}_{1}}$ are final and initial position respectively. It is a scalar quantity. It is a vector quantity. The distance covered by an object during the course of motion can never be negative or zero. It is always positive. The displacement of an object can be positive, negative or zero during the course of motion. The distance travelled is either equal to or greater than displacement and is never less than magnitude of displacement. The magnitude of displacement is less than or equal to the distance travelled during the course of motion. The distance is dependent upon the path travelled by the object. The magnitude of displacement is not dependent on the path taken by an object during the course of motion.

Difference Between Speed and Velocity:

 Speed Velocity It refers to the total path length travelled divided by the total time interval during which the motion has taken place. It refers to the change in position or displacement divided by the time intervals, in which this displacement occurs. It is a scalar quantity. It is a vector quantity. It is always positive during the course of the motion. It may be positive, negative or zero during the course of the motion. It is greater than or equal to the magnitude of velocity. It is less than or equal to the speed.

Note:

When the motion of an object is along a straight line and in the same direction, the magnitude of displacement is the same as the total path length.

In this case, the magnitude of average velocity is equal to the average speed. However, this is not always the case. The average velocity gives an idea on how fast an object has been moving over a given interval but does give an idea on how fast it moves at different instants of time during that interval.

5. Scalar and Vector Quantities:

5.1 Scalar quantities:

• The physical quantities that have only magnitude but no direction, are termed scalar quantities.

• Some examples of scalars are mass, length, time, distance, speed, work and temperature.

5.2 Vector quantities:

• The physical quantities that have magnitude as well as direction are termed vector quantities.

• Some examples of vectors are displacement, velocity, acceleration, force, momentum, torque.

6. Average Velocity and Average Speed:

6.1 Average velocity:

• It refers to the change in position or displacement divided by the time interval, in which the displacement occurs.

• The S.I. unit of velocity is $m/s$ even though $km/h$ is used in many daily life applications and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-1}}]$.

6.2 Average speed:

• It refers to the total path length travelled divided by the total time interval during which the motion has taken place.

• Its S.I. unit is $m/s$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-1}}]$.

7. Instantaneous Velocity and Instantaneous Speed:

7.1 Instantaneous velocity:

• It refers to the velocity at an instant $t$. Instantaneous velocity can further be expressed as the limit of the average velocity during which the time interval $\Delta t$ becomes infinitesimally small.

• Mathematically, instantaneous velocity $=Lt(\Delta x/\Delta t)=dx/dt$

• The quantity on the right-hand side of the above expression is the differential coefficient of $x$ with respect to $t$ and is represented by $dx/dt$.

• Clearly, it refers to the rate of change of position with respect to time at that particular instant.

• Its S.I. unit is $m/s$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-1}}]$.

7.2 Instantaneous Speed:

• Instantaneous speed or simply speed refers to the magnitude of velocity.

• Its S.I. unit is $m/s$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-1}}]$.

8. Acceleration:

8.1 Average Acceleration:

• The average acceleration over a time interval refers to the change of velocity divided by the time interval.

• Mathematically, it is given by $a=({{v}_{2}}-{{v}_{1}})/({{t}_{2}}-{{t}_{1}})$, where ${{v}_{2}}$ and ${{v}_{1}}$ are velocities at time ${{t}_{2}}$ and ${{t}_{1}}$ respectively.

• Average acceleration can thus be defined as the average change of velocity per unit time.

• Its S.I. unit is $m/{{s}^{2}}$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-2}}]$.

8.2 Instantaneous Acceleration:

• Mathematically, instantaneous acceleration can be expressed in the same way as the instantaneous velocity as follows:

$a=\underset{\Delta t\to 0}{\mathop{\lim }}\,(\Delta v/\Delta t)=dv/dt$

• Its S.I. unit is $m/{{s}^{2}}$ and its dimensions are $[{{M}^{0}}{{L}^{1}}{{T}^{-2}}]$.

• When there is uniform acceleration, obviously, instantaneous acceleration is the same as the average acceleration over that period of time.

• As velocity is a quantity involving both magnitude and direction, a change in the velocity may also involve either or both of these factors.

• Thus, acceleration may result from a change in the speed(magnitude), a change in direction or changes in both.

• Similar to velocity, acceleration can also be positive, negative or zero.

Note:

• We would restrict ourselves to the study of constant acceleration in this chapter. In this case, average acceleration is the same as the constant value of acceleration during a particular time interval.

• When the velocity of an object is ${{v}_{0}}$ at $t=0$ and $v$ at time $t$, we have

$a=\frac{v-{{v}_{0}}}{t-0}\Rightarrow v={{v}_{0}}+at$. This is nothing but the first equation of motion.

• Other equations of motion are:

$S={{v}_{o}}t+\frac{1}{2}a{{t}^{2}}$

${{v}^{2}}-{{v}_{0}}^{2}=2aS$

$S={{v}_{0}}+\frac{a}{2}(2n-1)$

In all these equations, acceleration is considered to be constant.

9. Graphs:

9.1 Uniform motion:

• If a body is said to be in uniform motion, the body completes equal distances in equal intervals of time.

• Here, velocity is constant during the course of motion.

• Also, acceleration is zero during the course of motion.

When we demonstrate this on the number line with x, v, a on the Y-axis and t on the X-axis, then we would have -

 Displacement-time graph Velocity-time graphVelocity = slope of $x-t$ graph Acceleration-time graph$\text{ac}{{\text{c}}^{\text{n}}}\text{= slope of }v-t\text{ graph}$ (i) Nature of slope: positiveMagnitude of slope: constant Nature of slope: zeroMagnitude of slope: constant Nature of slope of $a-t$ (ii) Nature of slope: negativeMagnitude of slope: constant Nature of slope: zeroMagnitude of slope: constant Nature of slope of $a-t$

9.2 Non-Uniform motion:

• If a body undergoes non-uniform motion, the body is said to be in uniformly accelerated motion.

• Here, the magnitude of velocity increases or decreases with the passage of time.

• Also, acceleration would not be zero as it undergoes accelerated motion.

When we demonstrate this on the number line with x, v, a on the Y-axis and t on the X-axis, then we would have -

 Displacement-time graph Velocity-time graphVelocity = slope of $x-t$ graph Acceleration-time graph$\text{ac}{{\text{c}}^{\text{n}}}\text{= slope of }v-t\text{ graph}$ (i) (ii) (iii) Nature of slope: positiveMagnitude of slope: Increasing Nature of slope: positiveMagnitude of slope: constant (iv) Nature of slope: positiveMagnitude of slope: decreasing Nature of slope: negativeMagnitude of slope: constant (v) Nature of slope: negativeMagnitude of slope: increasing Nature of slope: negativeMagnitude of slope: constant (vi) Nature of slope: negativeMagnitude of slope: decreasing Nature of slope: positiveMagnitude of slope: constant

Why Do You Need to Study CBSE Class 11 Physics Notes Chapter 2 Motion in a Straight Line?

• Motion in a straight line is a chapter you cannot afford to skip in physics as it forms the very basis of the entire subject.

• This CBSE Class 11 Physics Chapter 2 Notes Motion in a Straight Line will set fundamentals for students interested in pursuing a career in Physics.

• CBSE Class 11th physics chapter 2 notes are useful and dedicated entirely to the student's CBSE updated Syllabus

• State the condition where the distance and displacement of a moving object have the same magnitude.

• How can distance traveled be calculated from a velocity-time graph?

• What is the difference between one, two, and three dimensional motion?

• Distinguish between the following

• Distance and Displacement

• Speed and Velocity

• Explain the statement with an example “ The direction in which an object moves is given by the direction of the velocity of the object and not by the direction of acceleration”.

Physics Class 11 Chapter 2 Revision Notes are available online in PDF file for all students. It can be downloaded for free from Vedantu's official website and app for quick revision of all the crucial concepts and equations in a stress-free manner just before the exam. These notes are well-written by experienced Physics teachers who have sound knowledge of NCERT latest syllabus and Class 11 exam pattern. Motion in straight line class 11 notes help students understand which topics have high weightage in exams so they can study in a strategic way to obtain good marks in Class 11 exams.

These Notes Are Made Following the Latest CBSE Syllabus of Physics NCERT Books

1) Mechanics :

• Statics

• Kinematics

• Dynamics

2) Rest and Motion

• Defining Rest

• Defining Motion

• Rest and motion as relative

3) Defining Point/mass

4) Position, Distance, Displacement

5) Difference between :

• Distance and Displacement

• Speed and Velocity

• Scalar and Vector Quantities

• Average Velocity and Average Speed

•  Instantaneous Velocity and instantaneous speed

6) Acceleration

7) Graphics

8) Uniform Motion

9) Non-Uniform Motion

Conclusion

Physics Chapter 2 Class 11 notes are short and handy, written in easy to understand language by the experts. The experts have discussed all the above mentioned topics in a very elaborate manner. CBSE Class 11 Physics Notes Chapter 2 Motion in a Straight Line can be downloaded and read offline as well as in PDF Format to quickly revise the whole chapter just before the exam. These revision notes will help students understand various physics concepts  and is a perfect way to study for exams.

FAQs on Motion in a Straight Line Class 11 Notes CBSE Physics Chapter 2 (Free PDF Download)

1. Why do I need to study CBSE Class 11 Physics Notes Chapter 2 Motion in a Straight Line?

Class 11 chapter 2 physics notes are beneficial to clear the fundamentals of motion in a straight line as these concepts will help students in further studies and competitive exams. The notes consist of short and crisp summary of motion in a straight line class 11 which help students prepare for exams with good marks and understand the basics of motion in a straight line.

2. What all topics are covered in CBSE Class 11 Physics Notes Chapter 2 Motion in a Straight Line?

Class 11th physics chapter 2 notes consists of all the crucial concepts and equations that can come in exam in simple and fun language for the clear understanding of students. Some of the basic topics covered in these notes are:

• SI unit

• Dimensional Analysis

• Significant figures

• Velocity

• Force

• Absolute Errors

• Nature of Physical laws,

• Fundamental force in nature

3. What is a Point Mass?

A point mass is when an object covers a distance more than its own size, while is in the course of motion. Such an object can be called Point Mass.

4. What are the types of motion in Chapter 2 of Class 11 Physics?

There are various types of motion that are discussed in Chapter 2 of Class 11 Physics. These include rectilinear motion, circular motion, rolling motion, and oscillation. All of these have their unique characteristics and formulas that enable students to solve problems based on these types of motions. You will come across several laws and theorems based on these motions too. For more information regarding motion in a straight line, you can access Class 11 Physics Revision Notes for Chapter 2 - Motion in a Straight Line free of cost.

5. What is motion in a straight line according to Chapter 2 of Class 11 Physics?

Motion in a straight line can also be of many types. It can be unaccelerated or accelerated. Under this chapter specifically, we will deal with uniform acceleration for which a set of simple equations can be obtained. Relative velocity is also a new concept that is introduced. However, it is important to note that all objects are referred to as point objects in this chapter. This helps make calculations much easier although it is not very relevant in practical scenarios.

6. What is displacement?

Displacement is a physical quantity that is a metric of length. Its SI unit is metre. It is generally defined as the shortest distance between any two points. Displacement can be zero, unlike distance. Always remember that distance can be equal to displacement, but displacement can never be greater than distance. Students often go wrong in easy questions based on these concepts, which is why regular practice and revision are essential.

7. What is the average velocity and instantaneous velocity?

The average velocity and instantaneous velocity of a moving object are slightly different. Average velocity measures the speed of an object over a stipulated time interval but does not give exact specifications of each second. In order to know the speed of an object at a particular instant, we have to calculate its instantaneous velocity. Instantaneous velocity requires us to apply the principles of differentiation. For more notes on velocity, go to Class 11 Physics Revision Notes for Chapter 2 available on Vedantu website and app.

8. Can you define acceleration?

Acceleration is a physical quantity that refers to a change in velocity over time. However, since velocity involves both speed and direction, a change in either one of those parameters could result in the acceleration of a moving body. This acceleration can be uniform or non-uniform. You can even calculate acceleration by finding out the slope of a velocity-time graph. For Chapter 2 of Class 11 Physics though, students are mostly taught to solve problems pertaining to uniform acceleration.