Question

which example would contain only longitudinal waves? a crowd doing the wave at a sporting event an ultrasound that transmits soundwaves the waves formed by the ocean playing the guitar strings

Explanation:

• A crowd doing the wave at a sporting event: This is a transverse wave - the motion of the crowd (up and down) is perpendicular to the direction the wave (the "wave" itself) travels.
• An ultrasound that transmits soundwaves: Sound waves are longitudinal waves. In a longitudinal wave, the particles of the medium vibrate parallel to the direction of wave propagation. Ultrasound is a type of sound wave.
• The waves formed by the ocean: Ocean waves are a combination of transverse and longitudinal motion, but are generally considered as surface waves (a complex type, but with significant transverse - like motion of water particles).
• Playing the guitar strings: The vibration of guitar strings (the back - and - forth motion perpendicular to the length of the string) creates transverse waves on the string, and these in turn create sound (longitudinal) waves in the air. But the question is about the example that contains only longitudinal waves.

Answer:

an ultrasound that transmits soundwaves