Introduction
HSA Notes brings complete, exam-focused solved notes to help Class 11 (1st Year, HSSC-I) students score high marks in their FBISE Physics board exam.
This page covers Unit 3, Translatory Motion, prepared strictly according to the FBISE New Book (NBF) syllabus, covering definitions, equations of motion, free fall, projectile motion, momentum conservation, and collisions, along with fully solved MCQs, questions, and numericals from HSA Notes
Translatory Motion
Definition: A body is said to undergo translatory motion when it moves along a straight or curved path such that all particles of the body cover the same distance in the same time, and the orientation of the body remains unchanged throughout the motion.
Types of Translatory Motion:
- Rectilinear motion — motion along a straight line, such as a car moving on a straight road.
- Curvilinear motion — motion along a curved path, such as a ball thrown at an angle.
This chapter also distinguishes between kinematics, the study of motion without considering the forces causing it, and dynamics, the study of motion together with the forces responsible for it.
Equations of Motion
For a body moving with uniform acceleration, three key equations connect initial velocity, final velocity, acceleration, time, and displacement. These equations form the backbone of nearly every numerical in this unit. Here, vᵢ represents initial velocity and vf represents final velocity.
- vf = vᵢ + at
- S = vᵢt + ½at²
- 2aS = vf² − vᵢ²
Here, vᵢ is the initial velocity, vf is the final velocity, a is the uniform acceleration, t is the time taken, and S is the displacement. Students should be comfortable rearranging each equation to solve for any unknown variable, since board exam numericals frequently require finding time, acceleration, or displacement rather than final velocity alone.
Free Fall
Free fall is a special case of uniformly accelerated motion in which a body falls under the influence of gravity alone, with air resistance neglected. The acceleration due to gravity is taken as g ≈ 9.8 m/s², and by sign convention, upward motion is generally treated as negative while downward motion is treated as positive.
The standard equations of motion apply directly to free fall problems, with two simple substitutions: acceleration a is replaced with ±g depending on the direction of motion, and displacement S is replaced with height h. This gives:
- vf = vᵢ ± gt
- h = vᵢt ± ½gt²
- 2gh = vf² − vᵢ²
This allows all three equations of motion to be reused without needing to memorize separate formulas for falling or rising bodies.
Projectile Motion
A projectile is any object launched into the air and allowed to move under the influence of gravity alone after launch. Projectile motion is analyzed by splitting it into two independent components, since the horizontal and vertical motions do not affect one another.
Horizontal motion: The velocity remains constant throughout the flight, since there is no horizontal acceleration (a_x = 0).
Vertical motion: The motion is uniformly accelerated downward under gravity (a_y = g), behaving exactly like a free fall problem, with vᵢ as the initial vertical velocity component and vf as the final vertical velocity component at any instant.
From these two independent components, three key results are derived and frequently tested in numericals and long-response questions:
- Maximum height reached by the projectile
- Time of flight, the total time the projectile remains in the air
- Range, the horizontal distance covered before landing
Mastering the derivation of these three formulas, rather than memorizing them blindly, makes it far easier to adapt to variations in exam questions, such as projectiles launched from an elevated point.
Momentum Conservation
For an isolated system, one on which no external force acts, the law of conservation of momentum states that the total momentum of the system remains constant before and after any interaction between its parts. This principle is one of the most fundamental laws in Physics and appears repeatedly in later chapters as well.
Applications of momentum conservation include analyzing collisions between two or more bodies and explaining the working principle of rockets, where the backward ejection of exhaust gases produces a forward thrust on the rocket in accordance with conservation of momentum.
Collisions
Collisions between bodies are classified into two main types based on whether kinetic energy is conserved during the interaction.
- Elastic collisions — both momentum and kinetic energy (KE) are conserved. The bodies separate after collision without any permanent deformation or heat loss.
- Inelastic collisions — momentum is conserved, but kinetic energy is not conserved, since some energy is converted into heat, sound, or deformation during the collision.
HSA Notes Features
- Complete solved MCQs based on the FBISE paper pattern
- Short and comprehensive questions with clear answers
- Solved numericals with full working and correct units
- Solved textbook exercises covering every question
- Assignments and practice questions for self-assessment and revision
- Full Translatory Motion notes for Class 11 available in PDF form at hsanotes.com
Why This Unit Matters
Translatory Motion is where students first apply mathematics directly to real physical motion, and the three equations of motion introduced here reappear, in modified form, throughout Circular Motion, Work & Energy, and even later units involving oscillations and waves.
Free fall and projectile motion are consistently among the most heavily tested topics in FBISE numericals, and a solid grasp of momentum conservation and collisions lays the groundwork for more advanced dynamics problems later in the course. Time invested in mastering this unit pays off across the entire syllabus.
Available Across All FBISE Institutions
These notes are built for students across all FBISE-affiliated schools and colleges, including Islamabad Model Colleges, F.G. Colleges, Army Public Schools & Colleges, Punjab Colleges, Dr. A.Q. Khan Colleges, Fazaia Inter Colleges, IMCB, IMCG, and Sir Syed Colleges.
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Frequently Asked Questions
What is the difference between rectilinear and curvilinear motion?
Rectilinear motion occurs along a straight line, such as a car on a straight road, while curvilinear motion occurs along a curved path, such as a projectile in flight.
How is free fall related to the standard equations of motion?
Free fall uses the same three equations of motion, with acceleration replaced by ±g and displacement replaced by height h, since gravity provides a constant, uniform acceleration.
Why is projectile motion analyzed using horizontal and vertical components separately?
Because the horizontal component of velocity remains constant with zero acceleration, while the vertical component accelerates under gravity, and treating them independently simplifies calculating maximum height, time of flight, and range.
What is the difference between elastic and inelastic collisions?
In an elastic collision, both momentum and kinetic energy are conserved, while in an inelastic collision, only momentum is conserved and some kinetic energy is converted into other forms of energy such as heat or sound.
Conclusion
With Unit 3, Translatory Motion, fully covered, Class 11 FBISE students now have a strong grasp of the equations of motion, free fall, projectile motion, and the principles of momentum conservation and collisions, all essential building blocks for the rest of the Physics syllabus. Practice the solved numericals and MCQs on this page alongside past papers, and consider joining our online classes for guided, exam-focused preparation, to build the accuracy and confidence needed for your board exam.
Best of luck for your Class 11 Physics exam!