1. The problem statement, all variables and given/known data What will be the speed of sound in a perfectly rigid body? Given : In a hypothetical situation we have a rigid body find the speed of sound when it passes through the material. Elasticity of medium = ∞ 2. Relevant equations velocity = √E/ρ ρ = density E = elasticity of medium 3. The attempt at a solution My attempt: An object which does not allow the movement of particles means that the particles in the body cannot vibrate which does not allow transfer of energy through the body. Hence sound will not travel through the body and hence the velocity of sound becomes 0. My teachers attempt: v = √∞/ρ v = ∞ My doubt : A wave cannot travel faster than the speed of light and when i asked my teacher as is this infinity referring to such a body not existing she said that it has a very high speed.