You want to describe the harmonic motion of a swing. you find out that it takes 2 seconds for the swing to complete one cycle. what is the swings period and frequency?

If it takes the swing 2 seconds to complete one cycle, then
that's the period of its motion ... 2 seconds.

The frequency is the reciprocal of the period ... 1/2 Hz.
('Hz' means 'per second'.)

Idon't understand is there supposed to be a list or something if there is pm or add in under this message i will do my best to .

D=m/v m=d*vd=densitym=massv=volumed(ether)=0.71 gr/cm³=0.71 gr/ mlv=130 mlm=d*vm=0.71 gr/ml*(130 ml)=92.3 gm=92.3 g