The gamma photons created during a pet scan are detected when they encounter a scintillator and produce a burst of light. this light is then turned into an electrical signal when it strikes a metal and an electron is emitted by means of the photoelectric effect. while this is not practical for actual medical applications, assume that the metal used in the detector is silver, with a work function of 4.7ev. planck's constant is 4.14×10−15ev⋅s. a) what is the minimum frequency light must have to eject an electron from the surface? a. 1.1×10^12 hzb. 1.2×10^19 hzc. 2.3×10^15 hzd. 1.1×10^15 hz

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?