hop on vs mount up

hop on

verb
  • Used other than figuratively or idiomatically: see hop, on. 

  • To begin playing a video game. 

  • To join a phone call or video call. 

mount up

verb
  • to increase over a period of time; to accumulate 

How often have the words hop on and mount up occurred in a corpus of books? (source: Google Ngram Viewer )