Answer:
kftisgkstisirstizurzursrus
Speed = (frequency) x (wavelength)
Speed = (19 per second) x (7 mm)
Speed = (19 x 7) (per second · mm)
<em>Speed = 133 mm/sec</em>
or you might want to write <em>Speed = 0.133 m/s</em> .
Ultraviolet rays can help us get vitamin D, but they can also damage or skin if w are exposed for too long.
Your answer is D.
The change in potential energy of an object is given by

where
m is the mass of the object
g is the gravitational acceleration

is the increase in altitude of the object
In our problem,

is the mass of the book,

and

is the increase in altitude of the book, so its variation of potential energy is