A valve is a flap of tissue that prevents blood from flowing back
The total momentum is unchanged according to the law of conservation of momentum. When the gun is fired, the bullet gains a high velocity forward (positive velocity), and that velocity multiplied by its mass is the momentum the bullet gains. Therefore, the gun must gain a momentum backwards to cancel out that momentum forward, so the gun recoils back with a negative velocity.
Higher pitched sounds produce waves which are closer together than for lower pitched sounds. A smaller triangle or cymbal will make a relatively higher pitch note
Compressions are the areas of high pressure while rarefractions are low pressure area
Wave D has the same wavelength as wave A, but the amplitude is lower. The answer is Wave D.
