An Overview of Ncert Books Class 11 Physics Chapter 4 Free Download
FAQs on Ncert Books Class 11 Physics Chapter 4 Free Download
1. Which topics from Chapter 4, Motion in a Plane, are most important for the Class 11 Physics exams in 2025-26?
For the Class 11 Physics exam, the most crucial topics from Motion in a Plane are:
Projectile Motion: This is a high-weightage topic. You must focus on deriving the equations for the path of a projectile, time of flight, maximum height, and horizontal range.
Uniform Circular Motion: Understanding the concepts of centripetal acceleration and force is essential. Questions are often asked to prove that it is an accelerated motion.
Vector Algebra: Questions on the triangle law and parallelogram law of vector addition, resolution of vectors, and the dot and cross products of vectors are frequently asked.
Relative Velocity: Conceptual questions and numericals, especially the 'rain-man' problems, are important.
2. What are some expected 3-mark and 5-mark questions from Motion in a Plane?
Based on CBSE exam patterns, here are some expected questions:
For 5 marks: A long-answer question could be to state the parallelogram law of vector addition and derive the expression for the magnitude and direction of the resultant vector. Another probable question is to show that the path of a projectile is a parabola and derive expressions for its time of flight and maximum horizontal range.
For 3 marks: A typical question might be to define centripetal acceleration and derive its formula (a = v²/r). You may also be asked to solve numerical problems based on projectile motion or relative velocity.
3. Which types of numericals are most frequently asked from the Motion in a Plane chapter?
The numerical problems from this chapter often test the application of formulas. Important types include:
Calculating the time of flight, maximum height, and horizontal range of a projectile given its initial velocity and angle of projection.
Problems on relative velocity, such as finding the direction a person should hold their umbrella in the rain or calculating the time taken for a boat to cross a river.
Calculating the resultant of two or more vectors using the parallelogram law or component method.
Finding the centripetal acceleration of an object in uniform circular motion, like a car on a circular track or a stone whirled in a circle.
4. Why is uniform circular motion considered an example of accelerated motion, even if the speed remains constant?
This is a key conceptual question. Uniform circular motion is considered accelerated motion because velocity is a vector quantity, possessing both magnitude (speed) and direction. While the speed of the object remains constant, its direction of motion changes at every point along the circular path. Since acceleration is defined as the rate of change of velocity, any change in velocity—whether in magnitude, direction, or both—results in acceleration. In uniform circular motion, the continuous change in direction creates a constant acceleration, known as centripetal acceleration, which is always directed towards the centre of the circle.
5. How are the concepts of scalar (dot) product and vector (cross) product important for exams?
Both products are crucial for scoring well. They are often tested through application-based questions:
The Scalar (dot) Product is important for finding the angle between two vectors and for calculating work done (Work = F · d) or power (Power = F · v). A common question is to prove that two vectors are perpendicular if their dot product is zero.
The Vector (cross) Product is used to find a vector that is perpendicular to the plane containing two other vectors. Its applications include calculating torque (Torque = r × F) and angular momentum. An expected question could be to find a unit vector perpendicular to two given vectors.
6. What is the significance of resolving a vector, and how is it applied in projectile motion?
Resolving a vector into its components is a fundamental technique used to simplify complex two-dimensional problems. Its significance lies in breaking down a vector (like force or velocity) into two or more perpendicular components that can be analysed independently. In projectile motion, this technique is critical:
The initial velocity vector 'u' is resolved into a horizontal component (u cosθ) and a vertical component (u sinθ).
This allows us to treat the complex 2D motion as two separate, simpler 1D motions: a horizontal motion with zero acceleration and a vertical motion with constant downward acceleration 'g'.
By analysing these components separately, we can easily derive the equations for trajectory, time of flight, and range, which is a frequently asked 5-mark derivation.
7. Can an object have zero velocity and still be accelerating?
Yes, this is a classic conceptual trap and an important one for exams. An object can have zero velocity momentarily while still being under acceleration. The most common example from this chapter relates to projectile motion. When a projectile is thrown upwards, at the highest point of its trajectory, its vertical velocity component becomes zero for an instant before it starts moving downwards. However, the acceleration due to gravity (g) is still acting on it, constantly pulling it downwards. Therefore, at the peak, its velocity is zero (only the horizontal component remains if projected at an angle), but its acceleration is non-zero (equal to 'g').
