Take the object's starting direction of motion to be the positive direction, so that a stopping force acts in the opposite direction. By Newton's second law, the object undergoes an acceleration <em>a</em> such that
-15 N = (20 kg) <em>a</em>
Solve for <em>a</em> :
<em>a</em> = - (15 N) / (20 kg) = -0.75 m/s²
The object's velocity <em>v</em> at time <em>t</em> is then given by
<em>v</em> = 3 m/s + (-0.75 m/s²) <em>t</em>
so the time it takes for the object to slow to a rest is
0 = 3 m/s + (-0.75 m/s²) <em>t</em>
<em>t</em> = (3 m/s) / (0.75 m/s²) = 4.0 s
B. Energy enters and exits the system matter does not
Explanation:
In thermodynamics, there are three types of system:
- Open system: it is a system that exchanges both matter and energy with the surroundings - an example is an open bottle
- Closed system: it is a system that exchanges only matter with the surroundings, while energy cannot enter and exit the system - an example is a closed bottle (air cannot enter/exit the bottle, but heat can be exchanged through the walls of the bottle)
- Isolated system: it is a system that cannot exchange matter or energy with the surroundings - an example is a sealed thermic container (heat cannot pass through the walls)
In this problem, we are asked to identify which statement best describes the island food web as a closed system: based on the definitions above, we can say that the correct option is
B. Energy enters and exits the system matter does not
Learn more about thermodynamics:
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Energy is the capacity to do some type of work
Answer:
The correct answer is - option A. The mashed potatoes will transfer heat into the gravy.
Explanation:
In this case, where Yamel heats the mashed potatoes but forgets to heat the gravy and put the cold gravy on the hot mashed potatoes. Heat always transfers from the high-temperature object to the low-temperature object. So the hot mashed potatoes will transfer the heat to the gravy according to option A. Cold is not a form of heat but the condition of absence of heat or very low temperature.
Thus, the correct answer is - option A. The mashed potatoes will transfer heat into the gravy.
