Answer:
Net force = 10 N in downward direction
Explanation:
Given that,
Upward force = 10 N
Downward force = 20 N
Let downward is negative and upward is positive.
Net force = 10+(-20)
= -10 N
So, the net force is 20 N and it is acting in downward direction.
Answer:
(The first law of thermodynamics) When you put a hot object in contact with a cold one, heat will flow from the warmer to the cooler. As a result, the warmer one will usually cool down and the cooler one will usually warm up. Eventually, they will reach the same temperature and heat flow will stop.
The first: alright, first: you draw the person in the elevator, then draw a red arrow, pointing downwards, beginning from his center of mass. This arrow is representing the gravitational force, Fg.
You can always calculate this right away, if you know his mass, by multiplying his weight in kg by the gravitational constant

let's do it for this case:

the unit of your fg will be in Newton [N]
so, first step solved, Fg is 637.65N
Fg is a field force by the way, and at the same time, the elevator is pushing up on him with 637.65N, so you draw another arrow pointing upwards, ending at the tip of the downwards arrow.
now let's calculate the force of the elevator

so you draw another arrow which is pointing downwards on him, because the elevator is accelating him upwards, making him heavier
the elevator force in this case is a contact force, because it only comes to existence while the two are touching, while Fg is the same everywhere