My course

Hi there! In part A, we are using U = mgh, where h = r and g = $\frac{GM}{r^2}$.

In Part B, we are saying Enet = Ecircle = -U + K.

U is negative to represent binding. Using centripetal force (Fg = Fc) to determine velocity, where Fg is Newtons law of gravity, we derive K = U/2.

The equation Enet = Ecircle = -U + K = -U + U/2 = -U/2.

In Part A we determine potential energy due to separation/height. In Part 2, we determine energy of orbit. The two equations are different based on how they are derived/reasoning behind each situation.

Hi there! I see that you reasoning is correct.

$v_{x}=v_{0x}=\frac{45m}{4.5s}=10\frac{m}{s}$

In vertical direction, Δy = -5m since we fall below launch point. I guess you missed this sign. You should get v_0y = 20.9 m/s or round to 21 m/s.

You simply decided to use v_0x and v_0y while the video chose to use v0sinθ and v0cosθ. You did not change anything in your approach.

Hi there! I don't see any issue with the answer. Did you apply Lenz's law?

Ensure you label the current on the loops to make following easy.