Two positively charged objects are separated by a large distance. One of the positively charged objects is replaced by a negatively charged object, and the two
objects are moved closer to each other.
Which of the following occurs in this situation?
a.
The attractive force becomes a repulsive force, which increases as the objects move closer
together.

B.
The repulsive force becomes an attractive force, which increases as the objects move closer to
each other.
C.
The attractive force becomes a repulsive force, which decreases as the objects move closer to
each other.
D.
The repulsive force becomes an attract
creases as the objects move closer to
each other.

Which of the following is an example of units for speed

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.

6–48 bananas are to be cooled from 24 to 138c at a rate of 215 kg/h by a refrigeration system. the power input to the refrigerator is 1.4 kw. determine the rate of cooling, in kj/ min, and the cop of the refrigerator. the specific heat of banana above freezing is 3.35 kj/kg·8c.