A machine gun fires n bullets per second, each of mass m with velocity v. The force on the gun is MCQ with Answer and Explanation

A machine gun fires n bullets per second, each of mass m with velocity v. The force on the gun is
A. ½ nmv
B. nmv²
C. nmv
D. nmv/t
Answer: Option C
Solution (By JKExamLibrary)
Force = rate of change of momentum = n × (mv) = nmv. This is average force required to hold gun.

This question belongs to: Science Physics

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A body executing SHM has amplitude 5 cm and time period 2 s. Maximum velocity is
A. 2.5π cm/s
B. 5π cm/s
C. 10π cm/s
D. 20π cm/s

Correct Answer: Option B


Explanation:
v_max = ωA = (2π/T) A = (2π/2)×5 = 5π cm/s.

This question belongs to: Science Physics
Question #2 Report Error
A lactometer operates on the principle of:
A. Newton's Law of Viscosity
B. Bernoulli's Theorem
C. Archimedes' Principle
D. Pascal's Law

Correct Answer: Option C


Explanation:
A lactometer is a specific type of hydrometer used to test the purity of milk by measuring its relative density. All hydrometers, including lactometers, work on Archimedes' Principle of buoyancy. They float at a depth that depends directly on the density of the liquid; they sink deeper in less dense liquids (like milk heavily diluted with water).

This question belongs to: Science Physics
Question #3 Report Error
What is the physical meaning of the 'Work Function' of a metal in the context of the photoelectric effect?
A. The maximum kinetic energy of an emitted electron.
B. The electrical resistance of the metal when light shines on it.
C. The minimum energy required to eject an electron from the metal surface.
D. The total energy of an incident photon.

Correct Answer: Option C


Explanation:
In Einstein's photoelectric theory, electrons are bound to the metal lattice. The 'work function' (often denoted by Phi or W) is defined strictly as the absolute minimum thermodynamic work (energy) needed to overcome these binding forces and remove an electron from the surface into a vacuum. If incident photon energy (hf) is less than the work function, absolutely no emission occurs.

This question belongs to: Science Physics