A book is sitting on a desk. What best describes the normal force acting on the book? the upward force the desk pushes on the book
the upward force the book pulls on the Earth
the downward force the book pushes on the desk
the downward force the Earth pulls on the book

Ultraviolet radiation is dangerous because it has a high enough energy to damage skin cells. what is the best explanation of the relationship between wavelength and wave energy? a) wave energy is related only to frequency, not wavelength. b) longer wavelengths have lower frequencies but higher energy. c) the shorter the wavelength, the lower the frequency and the higher the energy. d) the shorter the wavelength, the higher the frequency and the higher the energy.

According to piaget’s stages of cognitive development, the child does not differentiate between self and other objects. the child repeats rewarding activities, discovers new ways to get what he or she wants, and may have imaginary friends. which period is described?

Which of the following situations would produce an average velocity of zero? o a. a horse galloping in a field b. a round-trip to school and back o c. a trip, first to the moon, then onto mars o d. the criss-crossing path of a flying bug