Answer:
a) Particle has a constant speed of 4, b) Velocity and acceleration vector are orthogonal to each other, c) Clockwise, d) False, the particle begin at the point (0,1).
Step-by-step explanation:
a) Let is find first the velocity vector by differentiation:
![\vec v = \frac{dr_{x}}{dt} i + \frac {dr_{y}}{dt} j](https://tex.z-dn.net/?f=%5Cvec%20v%20%3D%20%5Cfrac%7Bdr_%7Bx%7D%7D%7Bdt%7D%20i%20%2B%20%5Cfrac%20%7Bdr_%7By%7D%7D%7Bdt%7D%20j)
![\vec v = 4\cdot \cos 4t\, i - 4 \cdot \sin 4t \,j](https://tex.z-dn.net/?f=%5Cvec%20v%20%3D%204%5Ccdot%20%5Ccos%204t%5C%2C%20i%20-%204%20%5Ccdot%20%5Csin%204t%20%5C%2Cj)
![\vec v = 4 \cdot (\cos 4t \, i - \sin 4t\,j)](https://tex.z-dn.net/?f=%5Cvec%20v%20%3D%204%20%5Ccdot%20%28%5Ccos%204t%20%5C%2C%20i%20-%20%5Csin%204t%5C%2Cj%29)
Where the resultant vector is the product of a unit vector and magnitude of the velocity vector (speed). Velocity vector has a constant speed only if magnitude of unit vector is constant in time. That is:
![\|\vec u \| = 1](https://tex.z-dn.net/?f=%5C%7C%5Cvec%20u%20%5C%7C%20%3D%201)
Then,
![\| \vec u \| = \sqrt{\cos^{2} 4t + \sin^{2}4t }](https://tex.z-dn.net/?f=%5C%7C%20%5Cvec%20u%20%5C%7C%20%3D%20%5Csqrt%7B%5Ccos%5E%7B2%7D%204t%20%2B%20%5Csin%5E%7B2%7D4t%20%20%7D)
![\| \vec u \| = \sqrt{1}](https://tex.z-dn.net/?f=%5C%7C%20%5Cvec%20u%20%5C%7C%20%3D%20%5Csqrt%7B1%7D)
![\|\vec u \| = 1](https://tex.z-dn.net/?f=%5C%7C%5Cvec%20u%20%5C%7C%20%3D%201)
Hence, the particle has a constant speed of 4.
b) The acceleration vector is obtained by deriving the velocity vector.
![\vec a = \frac{dv_{x}}{dt} i + \frac {dv_{y}}{dt} j](https://tex.z-dn.net/?f=%5Cvec%20a%20%3D%20%5Cfrac%7Bdv_%7Bx%7D%7D%7Bdt%7D%20i%20%2B%20%5Cfrac%20%7Bdv_%7By%7D%7D%7Bdt%7D%20j)
![\vec a = 16\cdot (-\sin 4t \,i -\cos 4t \,j)](https://tex.z-dn.net/?f=%5Cvec%20a%20%3D%2016%5Ccdot%20%28-%5Csin%204t%20%5C%2Ci%20-%5Ccos%204t%20%5C%2Cj%29)
Velocity and acceleration are orthogonal to each other only if
. Then,
![\vec v \bullet \vec a = 64 \cdot (\cos 4t)\cdot (-\sin 4t) + 64 \cdot (-\sin 4t) \cdot (-\cos 4t)](https://tex.z-dn.net/?f=%5Cvec%20v%20%5Cbullet%20%5Cvec%20a%20%3D%2064%20%5Ccdot%20%28%5Ccos%204t%29%5Ccdot%20%28-%5Csin%204t%29%20%2B%2064%20%5Ccdot%20%28-%5Csin%204t%29%20%5Ccdot%20%28-%5Ccos%204t%29)
![\vec v \bullet \vec a = -64\cdot \sin 4t\cdot \cos 4t + 64 \cdot \sin 4t \cdot \cos 4t](https://tex.z-dn.net/?f=%5Cvec%20v%20%5Cbullet%20%5Cvec%20a%20%3D%20-64%5Ccdot%20%5Csin%204t%5Ccdot%20%5Ccos%204t%20%2B%2064%20%5Ccdot%20%5Csin%204t%20%5Ccdot%20%5Ccos%204t)
![\vec v \bullet \vec a = 0](https://tex.z-dn.net/?f=%5Cvec%20v%20%5Cbullet%20%5Cvec%20a%20%3D%200)
Which demonstrates the orthogonality between velocity and acceleration vectors.
c) The particle is rotating clockwise as right-hand rule is applied to model vectors in 2 and 3 dimensions, which are associated with positive angles for position vector. That is:
And cosine decrease and sine increase inasmuch as t becomes bigger.
d) Let evaluate the vector in
.
![r(0) = \sin (4\cdot 0) \,i + \cos (4\cdot 0)\,j](https://tex.z-dn.net/?f=r%280%29%20%3D%20%5Csin%20%284%5Ccdot%200%29%20%5C%2Ci%20%2B%20%5Ccos%20%284%5Ccdot%200%29%5C%2Cj)
![r(0) = 0\,i + 1 \,j](https://tex.z-dn.net/?f=r%280%29%20%3D%200%5C%2Ci%20%2B%201%20%5C%2Cj)
False, the particle begin at the point (0,1).