Answer:
It should be fibre optic cable , buried underground
The coordinate system should have the origin at the point where the feather is dropped and the downward direction is to be taken as positive.
All falling bodies experience acceleration towards the center of the Earth due to the force of gravitational attraction exerted on the object by the Earth. A feather, when dropped experiences an acceleration in the downward direction. Since the acceleration of the feather is in the downward direction, a feather, when dropped with zero initial velocity, has its velocity vector directed in the direction of its acceleration.
If the downward direction is taken as positive, the falling feather can be said to have a positive velocity and a positive acceleration.
To solve this problem we will apply the concept of magnification, which is given as the relationship between the focal length of the eyepieces and the focal length of the objective. This relationship can be expressed mathematically as,

Here,
= Magnification
= Focal length eyepieces
= Focal length of the Objective
Rearranging to find the focal length of the objective

Replacing with our values


Therefore the focal length of th eobjective lenses is 27.75cm
Answer:
static coefficient = 0,203 & kinetic coefficient = 0,14
Explanation:
There are two (2) conditions, when the desk is about to move and when the desk is moving. In the attachements you can see the two free body diagram for each condition.
In the first condition, there is no movement and the force is 12 N, in the image we can see the total forces are equal to 0 and by the definition of the friction force we can get the static friction coefficient.
In the second condition there is movement in the direction of the force which is equal to 8 N, again by the definition of the friction force we can get the kinetic friction coefficient. Since the desk is moving with constant velocity there is not acceleration.
K.E.= 1/2 x MV^2 = 1/2 x 40(kg) x (25x25) =12500J