I just did this lol good luck
Answer:
The force the skater exerts is 50 N
Direction: towards wall
Explanation:
The impulse is equal to:

The average force is:

Where
vf = final speed = -1 m/s
vi = initial speed = 0
m = mass = 40 kg
Δt = time interval = 0.8 s
Replacing:
(force applied by the wall)
The force the skater exerts is
Fsk = -Fave = -(-50) = 50 N
Direction: towards wall
Not sure about the answer
The major innovators in the late nineteenth or early twentieth century isThomas Edison Alexander Graham Bell
Answer:
Velocity in the smaller pipe should not be included as an additional variable.
Explanation:

The dimensional formula of the variables are

Now using Buchingham's Pi Theorem, 6 - 3 = 3 dimensional parameters are required.
Use, D_1, V, \mu as the repeating variables.
Therefore, 

From this
1+c=0
-2+a+b-2c=0
-b+c=0
c=-1, b = -1, a = 1
Now, 
For 

c = 0
1 + a + b - 2c = 0
-b + c = 0
Therefore, a = -1, b = 0, c = 0

For 


1 + c = 0
-4 + a + b - 2c = 0
2-b+c=0
c=-1, b=1, a = 1
Therefore, 
Now checking,

Therefore, 
From continuity equation


is not independent of 
Therefore it should not be included as an additional variable.