Answer:
Potential energy plus kinetic energy equals mechanical energy because mechanical energy is basically just all of an object's energy, it's just two kinds of energy. The potential is stored inside and kinetic is being used. Both of those together is the total amount of the objects energy, which is the mechanical energy.
Explanation:
The first law of thermodynamics can be written as

where

is the variation of internal energy of the system

is the amount of heat absorbed by the system

is the work done by the system on the surrounding.
Using this form, the sign convention for Q and W becomes:
Q > 0 --> heat absorbed by the system (because it increases the internal energy)
Q < 0 --> heat released by the system (because it decreases the internal energy)
W > 0 --> work done by the system (for instance, an expansion: when the system expands, it does work on the surrounding, and so the internal energy decreases, this is why there is a negative sign in the formula Q-W)
W < 0 --> work done by the surrounding on the system (for instance, a compression: when the system is compressed, the surrounding is doing work on the system, and so the internal energy of the system increases)
Answer:

Explanation:
First, let's find the voltage through the resistor using ohm's law:

AC power as function of time can be calculated as:
(1)
Where:

Because of the problem doesn't give us additional information, let's assume:

Evaluating the equation (1) in t=3600 (Because 1h equal to 3600s):

<span>h ( t) = h(1 sec) = -16t^2 + 541
so h (2 sec) = -16*(2)^2 + 541 = -64 + 541 = <span>477 ft
Therefore, </span></span>the height of the rock after 2 seconds is 477 feet.
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