Lesson 7 – Momentum & Collisions
Phase 3: Exam Mastery
Page 8 – Previous IIT / JEE Objective Questions (Level-2)
These questions are inspired by actual IIT-JEE patterns. Focus is on conceptual clarity, elimination, and calm thinking.
Q1. (IIT-JEE)
Two bodies collide elastically in one dimension. If the velocity of approach is zero, then after collision:
- A) Both bodies remain at rest
- B) Velocities are exchanged
- C) Collision cannot take place
- D) Kinetic energy increases
✔ Correct Answer: C
Trick: No approach → no collision.
Q2. (JEE Main)
A ball falls vertically on a floor and rebounds. If the coefficient of restitution is e, the ratio of times of ascent and descent is:
- A) e
- B) e²
- C) 1/e
- D) 1
✔ Correct Answer: A
Tip: Time ∝ velocity, height ∝ velocity².
Q3. (IIT-JEE Advanced)
In an elastic collision between two particles, which quantity remains unchanged for each particle when viewed from the centre-of-mass frame?
- A) Velocity
- B) Speed
- C) Momentum
- D) Kinetic energy
✔ Correct Answer: B
Examiner Trap: Direction changes, speed does not.
Q4. (JEE Main)
A bullet embeds into a block resting on a smooth surface. Which of the following is conserved during collision?
- A) Kinetic energy
- B) Mechanical energy
- C) Linear momentum
- D) Velocity
✔ Correct Answer: C
Rule: External horizontal force = 0.
Q5. (IIT-JEE)
A system has zero initial momentum. After an internal explosion, the total momentum becomes:
- A) Maximum
- B) Zero
- C) Negative
- D) Depends on mass distribution
✔ Correct Answer: B
Golden Law: Internal forces cannot change total momentum.
🧠 Speed-Solving Tips (Objective-2)
✔ If approach velocity = 0 → no collision
✔ Bounce problems → remember e² (height), e (time)
✔ Centre-of-mass frame removes complexity
✔ Explosion → momentum stays zero
✔ Look for ONE correct option, not all logic
📌 Next
Next page will include:
✔ Multi-correct IIT questions
✔ Assertion–Reason type
✔ Very high-trap MCQs
👉 Next: Objective 3 (Page 9)
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