Answer:
d = 0.544 m
Explanation:
To solve this problem we must work in two parts: one when the surface has no friction and the other when the surface has friction
Let's start with the part without rubbing, let's find the speed that the box reaches., For this we use the conservation of mechanical energy in two points: maximum compression and when the box is free (spring without compression)
Initial, maximum compression
Em₀ = Ke = ½ k x²
Final, free box without compressing the spring
= K = ½ m v²
Emo = 
½ k x² = ½ m v²
v = √ (k / m) x
Let's reduce the SI units measures
x = 20 cm (1m / 100cm) = 0.20 m
v = √ (100 / 2.5) 0.20
v = 1,265 m / s
Let's work the second part, where there is friction. In this part the work of the friction force is equal to the change of mechanical energy
= ΔEm =
- Em₀
= - fr d
Final point. Stopped box
= 0
Starting point, starting the rough surface
Em₀ = K = ½ m v²
With Newton's second law we find the force of friction
fr = μ N
N-W = 0
N = W = mg
fr = μ mg
-μ m g d = 0 - ½ m v²
d = ½ v² / (μ g)
Let's calculate
d = ½ 1,265² / (0.15 9.8)
d = 0.544 m
Answer: v = 
Explanation: q = magnitude of electronic charge = 
mass of an electronic charge =
V= potential difference = 4V
v = velocity of electron
by using the work- energy theorem which states that the kinetic energy of the the electron must equal the work done use in accelerating the electron.
kinetic energy =
, potential energy = qV
hence, 

Point of reference - an indicator that orients you generally; "it is used as a reference for comparing the heating and the electrical energy involved"
Now for this problem, what is given is a 40 Newtons which would represent the force to be applied to the object, and a distance of 10 meters after the application of the said force. When these two combine, work is done. The unit for work is Joules and this is what we are looking for. The formula to get Joules or for work would be the force applied to the object multiplied by the distance that it travelled after the application of the force. It looks like this
work = force x distance
Joules = Newtons x meter
so let us substitute the variables to their corresponding places
Joules = 40 N x 10 m
Joules = 400 J
So the answer to this question would be C. 400 J