A picture of weight 4N is supported by a string on a nail as shown below. Find the tension on the strings at P and Q if the strings are each inclined at 80° to the
vertical.
80
:80
T
P
4N

you go to your settings preference and in the end youll see sth that says "i want to delete my acc" click on it and u'll acc will be deleted but u have to wait.

the part of the wave he is travelling on is the crest

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.