g A The box leaves position x=0 with speed v0. The box is slowed by a constant frictional force until it comes to rest at position x=x1. Find Ff, the magnitude of the average frictional force that acts on the box. (Since you don't know the coefficient of friction, don't include it in your answer.) Express the frictional force in terms of m, v0, and x1. View Available Hint(s) Ff = nothing Part B After the box comes to rest at position x1, a person starts pushing the box, giving it a speed v1.

 fr = m v₀² / 2 (x₁-x₀)

Explanation:

a) For this exercise we use Newton's second law  

X axis  

    - fr = ma  

Y Axis  

     N-W = 0  

     N=W

let's look for acceleration with expressions of kinematics  

      v² = v₀² - 2 a Δx  

at the point where stop v = 0

     a = v₀² / 2 Δx

let's replace  

     -fr = m (- v₀² / 2 (x₁-x₀))

      fr = m v₀² / 2 (x₁-x₀)

b)they ask for the same  

in this case part of rest  

v₁² = 0 + 2 a Δx  

a = v₁² / 2ΔX  

we write Newton's second law  

F - fr = m a  

fr = F - ma  

fr = F - m v₁² / 2Δx

they are non-matter

explanation:

they are non-matter. basically, any type of energy or any abstract concept is an example of something that does not matter. other examples include dreams, magnetism, radio, and hate

i think the answer would be b