10.9#6

Hi, I've been attempting this problem for some time and can't seem to get
it. I've been following the book's example to the letter. I first created a
parametric model for the projectile, where x=200cos(30)t, which simplifies
to 100sqrt(3)t. My y model was 200sin30 - (1/2)(9.8)t^2, which simplifies
to 100 - 4.9t^2. Setting this to 0 and solving gives the answer
sqrt(100/4.9) = t. I plugged this value into the x equation to get the
range, and the answer was marked incorrect. Can you explain what I did
wrong?

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OK, so your first mistake: you were trying to do too many things in your head. You should write out the steps. These involve a lot of integration: your starting ingredients should be a(t) = -9.8j, and v(0)=<200cos(30), 200sin(30)> and r(0) = <0,0>. Then you need to integrate twice using the fundamental theorem of calculus each time and substituting in v(0) and r(0) as appropriate.  From your answer it looks like you forgot to include the effect of v(0) in integrating out to r(t).