Assertion (A): The velocity of sound is greater in solids than in gases. Reason (R): Solids possess higher elasticity compared to gases. MCQ with Answer and Explanation
Assertion (A): The velocity of sound is greater in solids than in gases. Reason (R): Solids possess higher elasticity compared to gases.
A. Both A and R are true and R is the correct explanation of A.
B. A is false but R is true.
C. A is true but R is false.
D. Both A and R are true but R is NOT the correct explanation of A.
Answer: Option A
Solution (By JKSSB Mock Tests)
The velocity of sound in a medium is determined by the formula v = √(E/ρ), where E is the modulus of elasticity and ρ is the density. Although solids are denser, their modulus of elasticity (bulk modulus) is tremendously higher than that of gases, overwhelmingly compensating for the density. Hence, sound travels fastest in solids.
Explanation:
The fundamental law of conservation of momentum dictates that in a closed system with no external net forces, total linear momentum is always conserved regardless of the collision type. In an inelastic collision, some kinetic energy is converted into other forms of energy (like heat or sound or deformation work), meaning kinetic and total mechanical energy are explicitly NOT conserved.
A body of mass 5 kg is moving with velocity 10 m/s. A constant force acts on it for 2 seconds, changing its velocity to 20 m/s. The magnitude of the force is:
Explanation:
Using Newton's second law: F = ma. First find acceleration: a = (v - u)/t = (20 - 10)/2 = 5 m/s². Then F = 5 kg × 5 m/s² = 25 N. Alternatively, using impulse-momentum theorem: FΔt = mΔv ⇒ F×2 = 5×(20-10) ⇒ F = 50/2 = 25 N. Both approaches confirm. This problem integrates kinematics with dynamics. Exam tip: When time interval is given, impulse-momentum method is often faster. Such questions assess ability to select appropriate physics principles for problem-solving in time-constrained exams.
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