Answer:
t_{out} =
t_{in}, t_{out} = 
Explanation:
This in a relative velocity exercise in one dimension,
let's start with the swimmer going downstream
its speed is

The subscripts are s for the swimmer, r for the river and g for the Earth
with the velocity constant we can use the relations of uniform motion
= D / 
D = v_{sg1} t_{out}
now let's analyze when the swimmer turns around and returns to the starting point

= D / 
D = v_{sg 2} t_{in}
with the distance is the same we can equalize

t_{out} = t_{in}
t_{out} =
t_{in}
This must be the answer since the return time is known. If you want to delete this time
t_{in}= D / 
we substitute
t_{out} = \frac{v_s - v_r}{v_s+v_r} ()
t_{out} = 
The answer is A
Explanation: the conservation of matter means that the mass stays the same
Answer:

Explanation:
Torque is defined as the cross product between the position vector ( the lever arm vector connecting the origin to the point of force application) and the force vector.

Due to the definition of cross product, the magnitude of the torque is given by:

Where
is the angle between the force and lever arm vectors. So, the length of the lever arm (r) is minimun when
is equal to one, solving for r:

Answer:
conductor
Explanation:
A "conductor" is a material that allows the charges to pass freely from one body to the other. This causes a movement among the electrons and this means that<em> the charge will be passed entirely to the object receiving it.</em> This is also called <em>"conductive material."</em>
Examples of conductors are: <em>copper, aluminum, gold, silver, seawater, etc.</em>
The opposite of conductors are called "insulators." These do not allow the free movement of charges from one object to the other.
Examples of insulators: <em>plastic, rubber, paper, glass, wool, dry air, etc.</em>