LESSON–3 : MOTION IN A PLANE
ADDITIONAL MATERIALS – 9 (PART–3)
IIT PYQs – METHODS • TRICKS • SOLVING PROCEDURE
🔹 PYQ–20 (JEE ADVANCED – METHOD SWITCHING)
Question:
A projectile is projected with speed u at an angle θ.
Find its speed when it is at height h above the point of projection.
Correct Method:
- Use Energy Conservation
- Avoid time-based equations
Solution:
Initial kinetic energy = ½mu²
Loss in potential energy at height h = mgh
Final kinetic energy = ½mv²
½mu² − mgh = ½mv²
v = √(u² − 2gh)
Why this works:
Speed at a given height depends only on energy change, not on angle or time.
Exam Trick:
If speed at a certain height is asked → Energy method is fastest.
🔹 PYQ–21 (JEE MAIN – DATA FILTERING)
Question:
A body is projected horizontally with speed 20 m/s from a tower of height 80 m.
Find the time taken to reach the ground.
Correct Thinking:
- Ignore horizontal velocity
- Consider only vertical free fall
Solution:
h = ½gt²
80 = 5t²
t = 4 s
Trap Alert:
Horizontal speed is given to confuse.
🔹 PYQ–22 (JEE ADVANCED – RANGE WITHOUT FORMULA)
Question:
Two projectiles are fired with the same speed.
One at 40° and the other at 50°.
Compare their ranges.
Thinking Method:
- 40° and 50° are complementary angles
- Use symmetry
Answer:
Ranges are equal.
Shortcut:
Angles adding to 90° → Same range (no formula needed).
🔹 PYQ–23 (JEE ADVANCED – RELATIVE VELOCITY GEOMETRY)
Question:
Two bodies move with equal speeds v in perpendicular directions.
Find their relative speed.
Method:
- Draw velocity vectors tail-to-tail
- Use right-angled triangle
Answer:
Relative speed = √(v² + v²) = v√2
Why geometry?
Relative velocity is vector subtraction, not scalar subtraction.
🔹 PYQ–24 (JEE MAIN – SAME HEIGHT LOGIC)
Question:
Compare speeds of a projectile at two points on its path
having same vertical height.
Method:
- Use energy conservation
- Potential energy same at same height
Answer:
Speeds are equal.
Exam Rule:
Same height → Same speed (direction may differ).
🔹 PYQ–25 (JEE ADVANCED – TIME SYMMETRY)
Question:
Find the ratio of time taken by a projectile to go up
to the time taken to come down.
Answer:
Ratio = 1 : 1
Concept:
Projectile motion is symmetric about highest point.
🔹 PYQ–26 (JEE ADVANCED – ZERO COMPONENT TRAP)
Question:
At the highest point of projectile motion, which quantities are zero?
Correct Analysis:
- Vertical velocity = 0 ✔
- Horizontal velocity ≠ 0 ✖
- Acceleration ≠ 0 ✖
Common Mistake:
Assuming acceleration becomes zero.
🔹 PYQ–27 (JEE MAIN – VECTOR PATTERN)
Question:
If vectors A = (a, b) and B = (b, −a),
find the angle between them.
Solution:
Dot product = ab − ab = 0
Angle = 90°
Memory Trick:
(a, b) ⟂ (b, −a) always.
🔹 PYQ–28 (JEE ADVANCED – METHOD PRIORITY)
Question:
When should energy method be preferred over equations of motion?
Answer:
- When speed at a height is asked
- When time is not required
- When angle information is irrelevant
🧠 ULTIMATE IIT PROBLEM-SOLVING FLOW (PART–3)
- Identify what is asked (speed / time / range)
- Decide method:
- Height → Energy
- Time → Vertical motion
- Range → Symmetry or formula
- Relative motion → Vector geometry
- Ignore unnecessary data
- Solve cleanly, avoid over-calculation
- Cross-check physical meaning
✅ ADDITIONAL MATERIALS – 9 (PART–3) COMPLETED
(Elite Method Selection & Exam Intelligence)
Intermediate Physics Complete Notes – IIT JEE & Board Exams
This page contains complete Intermediate Physics notes along with IIT JEE materials, previous year questions, solved problems, diagrams, and exam strategies.
📘 Lesson 1: Units and Measurements
📘 Lesson 2: Motion in a Straight Line
📘 Lesson 3: Motion in a Plane
- Part 1
- Part 2
- Part 3
- Part 4
- Part 5
- Part 6
- Part 7
- Part 8
- Part 9
- Part 10
- Part 11
- Part 12
- Part 13
- Part 14
- Part 15
- Part 16
- Part 17
📌 This page is updated regularly with new lessons.
No comments:
Post a Comment