To calc this feat, I will use the formula for force of shearing, where shear force = area sheared x shear stress, shear stress being the tensile strength of the material x 0.6 (the modification factor for steels).
We'll use steel as the material for the spaceship (however, because this UFO apparently went into warp drive, it is likely something far stronger).
I will assume Juliet is as tall as the average US white woman i.e. 164.9 cm
Juliet = 1.649m = 76 pixels
Height of relevant parts of UFO = 300 pixels = 6.509 m
Length of middle section of UFO = 490 pixels = 10.632m
Length of UFO (min) = 1920 pixels = 41.659m
This is a visualization of how I got the area using the above conditions.
Outer area length = length of UFO - middle section length = 31.027m
Area of middle section = (10.632m)(6.509m)=69.204m^2
Area of outer triangles = (31.027m)(6.509m) = 201.963m^2
Total area = 271.167 m^2
We'll use the lowest tensile strength for steel (400 MPa):
Shear force = (0.6)(400x10^6 N/m^2)(271.167m^2)=6.508x10^10 Newtons
The force it was applied over was at least the height of the middle section since it was a downward slash so:
Work = (6.508x10^10 N)(6.509m) = 4.236x10^11 Joules
Give me some time to account for the area inside the spacecraft, however.
Edit: Apparently it was a near completely solid aircraft with a space at the top and bottom....welpHere is some proof of it being near filed wthin (pic related).
So 4.236 x 10^11 Joules = 101.24 tons of tnt = Low MCB
So stronger than RWBY