Highest velocity reached on a hill

[Drizzy]

How am I supposed to keep going when I don't understand. Can you explain the equation that is marked with the number 2 ?

 

[PeroK]

How am I supposed to keep going when I don't understand. Can you explain the equation that is marked with the number 2 ?

First, you wrote:

$F1 = sin(30)mg$

And just stop.

But, sin(30) = 1/2, so $F1 = mg/2$ That's not complicated!

Then you wrote:

F1 - force of friction = ma

And just stop. With 0.85F = force of friction, you have:

mg/2 - 0.85F = ma ...

As I suggested above, I think this problem is too long and complicated. I think you're not used to putting several ideas together. That said, it's not an easy problem and you can see by all those arrows that your teacher got into a bit of tangle trying to solve it!

Maybe someone else can step in, but I think I've shot my bolt on this.