Physics · Class 11 Science
Ch 2Motion in a Straight Line — Class 11 Physics, concept-first.
Before we can say anything meaningful about how a body moves, we must first answer the question "moving relative to what?" A cup sitting on a train table is at rest with respect to the train, but it is moving at, say, 80 km/h with respect to the ground, and moving even faster with respect to the Sun.
Key concepts
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Position, Path Length and Displacement
For an object moving along a straight line, its position at any instant is its coordinate on a number line fixed by a chosen origin and positive direction.
Most relevant Q&A
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Frame of Reference
Before we can say anything meaningful about how a body moves, we must first answer the question "moving relative to what?" A cup sitting on a train table is at rest with respect to the train, but it i…
Position, Path Length and Displacement
Position. For an object that moves along a straight line, we set up a number line: we fix an origin (the point ), a positive direction (conventionally to the right), and a unit of length.
Average Speed and Average Velocity
Once we can measure how far an object has travelled (path length) and by how much its position has changed (displacement) over an interval of time, we can define two related — but generally different…
Instantaneous Velocity and Instantaneous Speed
Average velocity, as defined in Section 2.3, describes the overall trend of motion across a whole time interval, but it cannot tell us how fast an object was moving at one particular moment.
Acceleration
Just as velocity measures the rate of change of position, acceleration measures the rate of change of velocity.
Position-Time Graphs
A position-time (x-t) graph plots the position of a body along the vertical axis against time along the horizontal axis.
Velocity-Time Graphs and Graphical Analysis
A velocity-time (v-t) graph plots the instantaneous velocity of a body along the vertical axis against time along the horizontal axis.
Kinematic Equations for Uniformly Accelerated Motion
For the common and important special case of uniformly accelerated motion — motion in which the acceleration has one constant value throughout the interval considered — three standard relations connec…
Relative Velocity in One Dimension
Every velocity we have discussed so far has implicitly been measured with respect to the ground (our chosen inertial frame, Section 2.1).
Summary
- Frame of reference: an origin, axes and a clock relative to which motion is described. A frame is inertial if Newton's first law holds in it (unaccelerated); an accelerating frame is non-inertial an…
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
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- Example 1A student walks 3 m due east from a point O and then walks back 3 m due west to O. Explain, with reference to the meanings of the two terms,…Free
- Example 2A car travels 400 m due east along a straight road in 20 s, then reverses direction and travels 150 m due west in 10 s. Find (a) the average…Free
- Example 3The position of a particle moving on the x-axis is given by $x(t) = 2 + 3t - t^2$ (x in metres, t in seconds). Find (a) its instantaneous ve…Preview
- Example 4The velocity of a particle moving in a straight line increases uniformly from 5 m/s to 25 m/s in 8 s. Using a velocity-time graph, find (a)…Preview
- Example 5A car moving at 30 m/s applies brakes that produce a uniform deceleration of 6 m/s². Using the kinematic equations, find the time taken by t…Preview
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- Q6Define an inertial frame of reference. Give one example of a non-inertial frame and explain briefly why Newton's laws of motion do not hold…Free
- Q7Is it possible for a body to have zero velocity at some instant and yet be accelerating at that very instant? Justify your answer with a sui…Free
- Q8Can the direction of the velocity of an object moving in a straight line be different from the direction of its acceleration? Explain with a…Free
- Q9What physical quantity is represented by (a) the slope of a position-time graph and (b) the slope of a velocity-time graph? Explain briefly.Preview
- Q10Explain, with reasoning, why the average speed of a body over a given time interval can never be less than the magnitude of its average velo…Preview
- Q11What physical quantity is represented by the area under a velocity-time graph? Justify your answer using the integral relationship between v…Preview
- Q12Explain the physical meaning of a negative acceleration (retardation) with the help of the example of a car slowing down as it approaches a…Preview
- Q13A body undergoes uniformly accelerated motion starting with velocity $u$ and constant acceleration $a$. Using calculus, show that its positi…Preview
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- Q14The position of a particle moving along the x-axis is given by $x(t) = 5t^2 - 3t + 2$ (SI units). Find expressions for its velocity and acce…Free
- Q15A ball is thrown vertically upward with an initial velocity of 20 m/s. Taking $g = 10\ \text{m/s}^2$, find (a) the maximum height reached an…Free
- Q16A train starts from rest and accelerates uniformly at 0.5 m/s² for 30 s. It then moves at the constant velocity so attained for 60 s, and fi…Free
- Q17Starting from $a = \dfrac{dv}{dt}$ and $v = \dfrac{dx}{dt}$, use calculus (the chain rule $a = v\,\dfrac{dv}{dx}$) to derive the kinematic r…Preview
- Q18A car decelerates uniformly from 25 m/s to rest in 5 s. Find (a) the magnitude of its deceleration and (b) the distance it travels while com…Preview
- Q19Two cars A and B travel in the same direction along a straight road with velocities 20 m/s and 15 m/s respectively. Find the relative veloci…Preview
- Q20Two cars move towards each other along the same straight road, one with a velocity of 20 m/s and the other with a velocity of 15 m/s. Find t…Preview
- Q21A stone is dropped from a height of 45 m above the ground. Taking $g = 10\ \text{m/s}^2$ and air resistance as negligible, find (a) the time…Preview
- Q22The position $x$ (in m) of a particle moving along a straight line was recorded at 1 s intervals: t = 0, 1, 2, 3, 4, 5 s gave x = 0, 2, 8, 1…Preview