Answer:
Objects between the source and observer produce possible shadows known as the umbra and the penumbra.
The umbra is a totally shadowed area, no light travels directly from the source to the observer.
The penumbra is a partially shadowed are where some of the source light travels directly to the observer an some of the source light is blocked from the observer (the object blocking the light is not a point object).
The question apparently refers to the differences seen by the observers.
C. Magnetism
It is a physical property, not a chemical property.
Answer:


Explanation:
We have an uniform circular motion, therefore, the pebble’s speed is given by the distance traveled in a revolution
and the period (T), since this is the time pebble’s takes to complete a revolution:

The period is inversely proportional to the frequency:

So, we have:

Recall that the radius is the half of the diameter and one revolution per is equal to one Hz:

The centripetal acceleration is defined as:

Not good with this but I’m gonna guess cell membrane?
Answer:
, 
Explanation:
The situation can be modelled by applying the Principle of Angular Momentum Conservation:

The final angular speed is:



The tangential velocities of the wheel and the clay are, respectively:



