Here's a tip: The unit of frequency ... Hertz or Hz ... means "per second". "Five times PER SECOND" is a frequency of 5 Hz.
The frequency of an object that vibrates five times every second is 5 Hz. Frequency measures the number of cycles per second, so 5 vibrations per second directly gives a frequency of 5 Hz. This indicates that the object completes 5 full cycles of vibration in one second.
;