You (mass 90 kg) are a spyentering a high-security building through a skylight 20 m above thef loor. Your partner is lowering you on a rope (total mass 10 kg,total length 25 m) and you need to tell her when to stop lowering you. You can’t shout up to her since that will alert security. So, you plan on tapping the rope. When she feels the tapping, she will stop lowering you.
How much time will pass between when you tap the rope and when shefeels it?