The internal energy of a system is always increased by __________. a adding heat to the system and having the system do work on
1 answer:
There are two correct options:
<span>d) a volume compression
e) adding heat to the system
In fact, we can have a look at the first law of thermodynamics:
</span>
<span>where
</span>
is the variation of internal energy
<span>Q is the heat absorbed by the system
W is the work done by the system on the surrounding
It is important to keep in mind the right sign convention for Q and W: Q is positive when the heat is absorbed by the system, while it is negative when it is released by the system; W is positive when it is done by the system on the surrounding, and negative when it is done by the surrounding on the system.
Using this convention, we can see that:
d) when there is a volume compression, the work is done by the surrounding on the system, so the work is negative, and the variation of internal energy is positive due to the negative sign -W in the first law of thermodynamics
e) when heat is added to the system, Q is positive, so the variation of internal energy is positive as well</span>
<span>d) a volume compression
e) adding heat to the system
In fact, we can have a look at the first law of thermodynamics:
</span>
<span>where
</span>
<span>Q is the heat absorbed by the system
W is the work done by the system on the surrounding
It is important to keep in mind the right sign convention for Q and W: Q is positive when the heat is absorbed by the system, while it is negative when it is released by the system; W is positive when it is done by the system on the surrounding, and negative when it is done by the surrounding on the system.
Using this convention, we can see that:
d) when there is a volume compression, the work is done by the surrounding on the system, so the work is negative, and the variation of internal energy is positive due to the negative sign -W in the first law of thermodynamics
e) when heat is added to the system, Q is positive, so the variation of internal energy is positive as well</span>
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Answer:
frequency
Explanation:
The phenomenon of apparent change in frequency due to the relation motion between the source and the observer is called Doppler's effect.
So, when we move farther, the frequency of sound decreases. The formula of the Doppler's effect is
where, v is the velocity of sound, vs is the velocity of source and vo is the velocity of observer, f is the true frequency. f' is the apparent frequency.
Answer:
v = 12.1 m/s
Explanation:
- When at the top of the circle, there are two forces acting on the combined mass of the rider and the motorcycle.
- These are the force of gravity (downward) and the normal force, which is directed from the surface away from it, perpendicular to the surface.
- In this case, as the motorcycle runs in the interior of the circle, at the top point this force is completely vertical, and is also downward.
- Since the motorcycle is moving in a vertical circle, there must be a force, keeping the object moving around a circle.
- This force is the centripetal force, aims towards the center of the circle, and is just the net force aiming in this direction at any point.
- At the top point, this force is just the sum of the normal force and the weight of the mass of the rider and the motorcycle combined, as follows (we take the direction towards the center as positive):
- Now, we know that the centripetal force is related with the tangential speed at this point and the radius of the circle as follows:
- Since the normal force takes any value as needed to make (1) equal to (2), if the speed diminishes, it will be needed less force to keep the equality valid.
- In the limit, when the motorcyvle tires barely touch the surface, this normal force becomes zero.
- In this condition, from (1) and (2), we can find the minimum possible value of the speed that still keeps the motorcycle touching the surface, as follows: