Ideal mechanical advantage doesn't take energy lost to friction into account. Explain why the mechanical advantage of a single fixed pulley is always 1. A single fixed pulley changes only the direction of the effort force. ... Energy transforms from the object supplying the force to the object being moved.
A) A concave mirror forming a larger, virtual image
Explanation:
The figure is missing; see attachment.
There are two types of mirror:
- Concave (converging) mirrors: a concave mirror is a mirror that reflects the light inward
- Convex (diverging) mirrors: a convex mirror is a mirror that reflects the light outward
The image formed by a mirror can also be of two types:
- Real image: it is formed on the same side of the object, with respect to the mirror
- Virtual image: it is formed on the opposite side of the object, with respect to the mirror
In the figure of this problem (see attachment), we see that:
- The mirror reflects the light from the object inward --> so it is a concave mirror
- The image is formed on the other side of the mirror --> it is a virtual image
So the correct option is
A) A concave mirror forming a larger, virtual image
Learn more about mirrors:
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1) Focal length
We can find the focal length of the mirror by using the mirror equation:

(1)
where
f is the focal length

is the distance of the object from the mirror

is the distance of the image from the mirror
In this case,

, while

(the distance of the image should be taken as negative, because the image is to the right (behind) of the mirror, so it is virtual). If we use these data inside (1), we find the focal length of the mirror:

from which we find

2) The mirror is convex: in fact, for the sign convention, a concave mirror has positive focal length while a convex mirror has negative focal length. In this case, the focal length is negative, so the mirror is convex.
3) The image is virtual, because it is behind the mirror and in fact we have taken its distance from the mirror as negative.
4) The radius of curvature of a mirror is twice its focal length, so for the mirror in our problem the radius of curvature is:
Different densities have to have a reason - different pressure and/or humidity etc. If there is a different pressure, there is a mechanical force that preserves the pressure difference: think about the cyclones that have a lower pressure in the center. The cyclones rotate in the right direction and the cyclone may be preserved by the Coriolis force.
If the two air masses differ by humidity, the mixing will almost always lead to precipitation - which includes a phase transition for water etc. It's because the vapor from the more humid air mass gets condensed under the conditions of the other. You get some rain. In general, intense precipitation, thunderstorms, and other visible isolated weather events are linked to weather fronts.
At any rate, a mixing of two air masses is a nontrivial, violent process in general. That's why the boundary is called a "front". In the military jargon, a front is the contested frontier of a conflict. So your idea that the air masses could mix quickly and peacefully - whatever you exactly mean quantitatively - either neglects the inertia of the air, a relatively low diffusion coefficient, a low thermal conductivity, and/or high latent heat of water vapor. A front is something that didn't disappear within minutes so pretty much tautologically, there must be forces that make such a quick disappearance impossible.