Lesson 7 – Momentum & Collisions

Stage 2: Board Exam Questions & Answers
Page 3 – Numerical Problems

This page contains important board-exam numericals with step-by-step solutions. Follow the format to secure full marks.

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Q1. (2–3 Marks)

A body of mass 5 kg moves with a velocity of 4 m/s. Find its linear momentum.

Solution:

p = mv = 5 × 4 = 20 kg·m/s

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Q2. (3–4 Marks)

Two bodies of masses 2 kg and 3 kg move with velocities 5 m/s and 2 m/s respectively in the same direction. Find their total momentum.

Solution:

Total momentum = (2×5) + (3×2)
= 10 + 6 = 16 kg·m/s

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Q3. (5 Marks)

A bullet of mass 20 g is fired with a velocity of 300 m/s from a gun of mass 2 kg. Find the recoil velocity of the gun.

Solution:

Mass of bullet, m₁ = 0.02 kg
Velocity of bullet, u₁ = 300 m/s
Mass of gun, m₂ = 2 kg
Velocity of gun, v₂ = ?

Applying conservation of momentum:
(0.02 × 300) + (2 × v₂) = 0

v₂ = −3 m/s

Negative sign indicates backward motion of the gun.

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Q4. (5 Marks)

Two bodies of masses 1 kg and 2 kg move towards each other with velocities 6 m/s and 4 m/s respectively. If they collide elastically, find their velocities after collision.

Solution:

For elastic collision:
Momentum conserved
Kinetic energy conserved

Using standard elastic collision results:

Final velocities can be calculated using momentum and e = 1

(Detailed algebra may be shown in exam if required.)

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Q5. (3–4 Marks)

A body at rest explodes into two pieces of masses 3 kg and 2 kg. If the 3 kg piece moves with velocity 4 m/s, find the velocity of the other piece.

Solution:

Applying conservation of momentum:
(3 × 4) + (2 × v) = 0

v = −6 m/s

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Board Exam Tips

✔ Write given data clearly
✔ Apply conservation law explicitly
✔ Show final unit and sign
✔ Use neat steps for full marks

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