The answer would be machines

**Answer:**

Answered

**Explanation:**

a) Two balls are at a distance of L/2 from the axis of rotation and one block at the center. ( center of rod).

therefore,

b) two balls at a distance L/4 at the from the axis and 1 ball at a distance 3L/4 from the from the axis.

=

A convergent meniscus lens is a lens that is composed of two spherical surfaces, like the on shown next:

The imaginary line that runs through the middle of the lens is the "symmetry axis".

In this type of lenses incident parallel beams of light converge in one point, as follows:

And thus we get the diagram.