On a trip you travel at a constant speed of 50 kilometers per hour North for 1 hour. Then you turn West and travel at a constant speed of 40 kilometers per hour for 2 hours. Calculate your velocity for the trip. 43 km per hour
31 km per hour
27 km per hour West + 17 km per hour North
50 km per hour North + 40 km per hour West

Glass is transparent to visibile light under normal conditions; however, at extremely high intensities, glass will absorb most of the light incident upon it. this works through a process known as multiphoton absorption. in this process, several photons are absorbed at the same time. if very intense light whose photons carry 2ev of energy is shined onto a material with a band gap of 4ev, that light can be absorbed through two-photon absorption, because two photons have the right amount of energy to bridge the band gap. what is the minimum number of photons of 800-nm light that are needed to equal or exceed the band gap of fused silica glass

Ascientist notices that an oil slick floating on water when viewed from above has many different colors reflecting off the surface, making it look rainbow-like (an effect known as iridescence). she aims a spectrometer at a particular spot and measures the wavelength to be 750 nm (in air). the index of refraction of water is 1.3

Which system of units is used by only a small number of countries in the world, including the u.s.