On an ice skating rink, a girl of mass 50 kg stands stationary, face to face with a boy of mass 80 kg. the children push off of one another, and the boy moves away with a velocity of +3 m/s. what is the final velocity of the girl? –1.9 m/s +1.9 m/s –4.8 m/s +4.8 m/s

4. who was the first one to measure the speed of light and conclude that it is finite? 5. who was the first philosopher who thought the speed of light is finite? 13. what is the speed of light numerically? 14. give an example of something moving faster than light 15. give an example for some particles or waves that

Some material consisting of a collection of microscopic objects is kept at a high temperature. a photon detector capable of detecting photon energies from infrared through ultraviolet observes photons emitted with energies of 0.3 ev, 0.5 ev, 0.8 ev, 2.0ev, 2.5ev, and 2.8ev. these are the only photon energies observed. (a) draw and label a possible energy-level diagram for one of the microscopic objects, which has four bound states. on the diagram, indicate the transitions corresponding to the emitted photons. explain briefly. (b) would a spring–mass model be a good model for these microscopic objects? why or why not? (c) the material is now cooled down to a very low temperature, and the photon detector stops detecting photon emissions. next, a beam of light with a continuous range of energies from infrared through ultraviolet shines on the material, and the photon detector observes the beam of light after it passes through the material. what photon energies in this beam of light are observed to be significantly reduced in intensity (“dark absorption lines”)? explain briefly.

How will the system respond to a temperature increase?