a yoyo in someones hand is an example of potential energy
Yes.
In fact, from the graph we see that the threshold frequency (the minimum energy of the incoming energy needed to extract a photoelectron from the material) is 
(we see it because this is the frequency at which the maximum kinetic energy of the emitted electron is zero).
The incoming photon in this problem has a frequency of 8.0 E14 Hz, so above the threshold frequency, therefore it is enough to extract photoelectrons from the material.
Answer:
The answer is below
Explanation:
Because of the resistance of transmission lines, high current along the line leads to large voltage drop. This voltage drop causes low efficiency because the voltage at the receiving end is far less than that at the sending end.
Therefore there is need to transmit at a higher voltage (smaller current) than that required by distribution because of efficiency.
Hence, For safety and efficiency, the voltage must be large in the transmission lines and small in the distribution lines.
I think the elevation of Y and Z are the following:
<span>Y=3200,
Z=2900 </span>
