Esteban pulls a 62 kg sled trough the snow. On the back of the sled is his 50 kg sack of fishing equipment. The  between the sled and the snow is 0.07 and the  between the sled and the sack is 0.1. While pulling, the fishing rod sticking out of his sack catches a tree branch, but Esteban doesn't notice and keeps walking. What force does Esteban need to exert to keep the sled moving with a constant velocity while the sack is pulled back across it?

F = 144 N

Explanation:

For this exercise we will use Neqwton's second law. Let's fix a reference system with the x-axis in the direction of the sled, let's write the forces for each part

Sack, let's use subscript 1

Y axis  

       N₁-W₁ = 0

       N₁ + W₁ = m₁ g

X axis

       fr₁ = m a₁

the expression for the friction force is

       fr = μ₁ N₁

     

we substitute

        μ₁ m₁ g = m a₁

         

Sled, subscript 2

Y axis

       N₂ - W₁ -W₂ = 0

       N₂ = W₁ + W₂

       N₂ = (m₁ + m₂) g

X axis

       F - fr₁ -fr₂ = m a₂

       

the expression for the deroce force is

      fr = μ N

we substitute

       F - μ₁ m₁g - μ₂ (m₁ + m₂) g = m a₂

as it indicates that the velocity is constant the acceleration of the sled is zero (a₂ = 0)

       F = μ₁  m₁g + μ₂  (m₁ + m₂) g

       F = g (m₁ (μ₁ + μ₂) + μ₂ m₂)

       

let's calculate

       F = 9.8 (50 (0.07 + 0.1) + 62 0.1)

       F = 144 N

Decomposers contribute to the nitrogen cycle by breaking down organic materials to return nitrogen into environment in different forms. they may break down bodies of  dead organisms result in nitrogen being returned to the soil as ammonia. in some instances, denitrifying bacteria in the soil break down nitrates return nitrogen into the air