A series of waves has a frequency of 3.5 Hz. Determine the period of a single wave.

I have no idea what substance it is that comprises that block.
But whatever it is, you've told me that every cubic meter of it
has 4,000 kg of mass. And I have no reason to doubt you.

So if I were to chip off a little 0.09-m³ piece of that block,
I know its mass would be 0.09 of 4,000 kg. That's 360 kg.

The weight of any mass is (mass) x (gravity), and if we're doing
all of this on Earth, then gravity = 9.8 m/s² . So the weight of my
chip off the old block is

= (mass) x (gravity)
= (360 kg) x (9.8 m/s²) = 3,528 Newtons. (about 794 pounds)