Well dark matter is , in a layman terms just a concept used to identify missing mass in the universe. (extremely simplified and probably wrong but look that up). It could be but then if it is then we would still be able to percive the matter in some form. All we know from instruments is that they have mass and absorb light. We would need more info before any conclusions but it is 100% a possibility. But remember that when someone says "3-d" for example they are talking about a certain space.. technically matter exists on all planes (at least all the planes we know of in our local universe.) The laws of the cosmos are not yet proven to be constant and even if they are what of outside it?
When you take high school physics ask your teacher.
They prefer leaves i believe
"Hydro..." means "water". Hydroelectric plants use the kinetic energy
of falling water to produce electrical energy.
I wouldn't exactly say that they "use water", because after they produce
the electrical energy, there's still just as much water as there was before.
Answer with Explanation:
We are given that
String makes an angle w.r.t vertical=
a.We have to derive an expression for the magnitude of the acceleration of the van in terms of the angle 
and magnitude g of the acceleration due to gravity.
According to newton's second law
b.
c.Velocity=Constant
We have to find the angle
