Answer:
Because winding roads have a gentle slope on hills, so it's easy to climb it than a steepy.
It is round or say spherical to widen the range of photography and it is designed to focus the image as the ray are coming from infinity so !!
I am not an expert of camera but ya it is the main theme !!
Answers:
a) 
b) 
Explanation:
a) Since we are told the satellites circle the space station at constant speed, we can assume they follow a uniform circular motion and their tangential speeds
are given by:
(1)
Where:
is the angular frequency
is the radius of the orbit of each satellite
is the period of the orbit of each satellite
Isolating
:
(2)
Applying this equation to each satellite:
(3)
(4)
(5)
(6)
(7)
(8)
Ordering this periods from largest to smallest:

b) Acceleration
is defined as the variation of velocity in time:
(9)
Applying this equation to each satellite:
(10)
(11)
(12)
(13)
(14)
(15)
Ordering this acceerations from largest to smallest:

Answer:
A) The crossbeam is moving relative to the observer on the platform so the height appears contracted.
Explanation:
The observer on the train and the beam are in the same reference frame. That means observer on the train will measure the proper length of the beam not the contracted length . the observer is outside and the plank is in the moving system,it will appear to be moving.
The density of the material would be
25/6 grams per cm^3.
to obtain the result above this is what we do:
density is calculated as: (the mass of the given material or object) / volume of the material
which leads us to 50grams /12cm^3