Answer:
a)
, b)
, c)
,
.
Step-by-step explanation:
a) The function in terms of time and the inital angle measured from the horizontal is:
![\vec r (t) = [(v_{o}\cdot \cos \theta)\cdot t]\cdot i + \left[(v_{o}\cdot \sin \theta)\cdot t -\frac{1}{2}\cdot g \cdot t^{2} \right]\cdot j](https://tex.z-dn.net/?f=%5Cvec%20r%20%28t%29%20%3D%20%5B%28v_%7Bo%7D%5Ccdot%20%5Ccos%20%5Ctheta%29%5Ccdot%20t%5D%5Ccdot%20i%20%2B%20%5Cleft%5B%28v_%7Bo%7D%5Ccdot%20%5Csin%20%5Ctheta%29%5Ccdot%20t%20-%5Cfrac%7B1%7D%7B2%7D%5Ccdot%20g%20%5Ccdot%20t%5E%7B2%7D%20%5Cright%5D%5Ccdot%20j)
The particular expression for the cannonball is:
![\vec r (t) = \left[(90\cdot \cos \theta)\cdot t \right]\cdot i + \left[(90\cdot \sin \theta)\cdot t -6\cdot t^{2} \right]\cdot j](https://tex.z-dn.net/?f=%5Cvec%20r%20%28t%29%20%3D%20%5Cleft%5B%2890%5Ccdot%20%5Ccos%20%5Ctheta%29%5Ccdot%20t%20%5Cright%5D%5Ccdot%20i%20%2B%20%5Cleft%5B%2890%5Ccdot%20%5Csin%20%5Ctheta%29%5Ccdot%20t%20-6%5Ccdot%20t%5E%7B2%7D%20%5Cright%5D%5Ccdot%20j)
b) The components of the position of the cannonball before hitting the ground is:


After a quick substitution and some algebraic and trigonometric handling, the following expression is found:





The angle for a maximum horizontal distance is determined by deriving the function, equalizing the resulting formula to zero and finding the angle:





Now, it is required to demonstrate that critical point leads to a maximum. The second derivative is:


Which demonstrates the existence of the maximum associated with the critical point found before.
c) The equation for the vertical component of position is:

The maximum height can be found by deriving the previous expression, which is equalized to zero and critical values are found afterwards:




Now, the second derivative is used to check if such solution leads to a maximum:

Which demonstrates the assumption.
The maximum height reached by the cannonball is:

