Why hot air balloon rises up in air n large ships Floyd in water

Hot air is less dense than cool air; the heated air causes the balloon to rise simply because it is lighter than an equal volume of cold air.So hot air balloon rises up in air.

Large ships float in water as their density is lesser than the water so.

concave lenses are used here. they spread the light out before it reaches the convex lens in the eye, therefore letting the image focus directly on the retina. hyperopia is known to you probably as farsightedness.

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this