Which law explains the recoil of a gun when a bullet is fired? MCQ with Answer and Explanation

Which law explains the recoil of a gun when a bullet is fired?
A. Newton's second law
B. Newton's first law
C. Law of conservation of energy
D. Newton's third law
Answer: Option D
Solution (By JKExamLibrary)
Recoil is due to action-reaction pair: gun exerts forward force on bullet, bullet exerts backward force on gun. Newton's third law states for every action there is equal and opposite reaction. Conservation of momentum also explains recoil, but the immediate law is third law. Gun recoil velocity is calculated using conservation of momentum derived from third law.

This question belongs to: Science Physics

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Question #1 Report Error
A satellite is orbiting close to Earth's surface. Its orbital speed is (g = 10 m/s², R = 6400 km)
A. 8 km/s
B. 4 km/s
C. 11.2 km/s
D. 16 km/s

Correct Answer: Option A


Explanation:
v = √(gR) = √(10×6400×10³) = √(64×10⁶) = 8×10³ m/s = 8 km/s. Escape velocity 11.2 km/s.

This question belongs to: Science Physics
Question #2 Report Error
The phenomenon of echo is based on which property of sound?
A. Interference
B. Reflection
C. Refraction
D. Diffraction

Correct Answer: Option B


Explanation:
Echo is the reflection of sound waves from a rigid surface, returning to the listener after a time delay. For distinct echo, minimum distance to reflector is about 17 m (so time delay > 0.1 s, persistence of hearing). Refraction bends sound in media with varying density; interference combines waves; diffraction bends around obstacles. Memory tip: 'Echo = sound reflection like light in mirror'. This application-based question links wave properties to daily-life phenomena, frequently tested in competitive exams to assess conceptual clarity beyond definitions. Always distinguish echo from reverberation (multiple reflections).

This question belongs to: Science Physics
Question #3 Report Error
When white light passes through a glass prism, it splits into a spectrum of seven colors. Which color deviates the least?
A. Red
B. Violet
C. Blue
D. Yellow

Correct Answer: Option A


Explanation:
Dispersion occurs because different colors of light travel at slightly different speeds inside the glass prism, meaning they have different refractive indices. Red light has the longest wavelength, the lowest refractive index in glass, and therefore deviates (bends) the least. Violet has the shortest wavelength and deviates the most.

This question belongs to: Science Physics