i need to find the velocity vector two results ! help please

mimi.janson

1. The problem statement, all variables and given/known data

find the velocity vector for the time t=2s

i have given r(t)=
(50*sin((1/2)*t)*cos ((1/4)t),
-50*sin((1/2)*t)*sin((1/4)t))

2. Relevant equations

i also know that r(t)=
(50*sin(k*t)*cos (1/2k*t),
-50*sin(k*t)*sin(1/2k*t))
where k = 0,5s^-1

3. The attempt at a solution
so i tried solving it and my attempt is shown in the attachment where i got the result
v(2)=6,8;-15,7

but someone said it has to be solved with the following results
25m/s*[0,272449, -0,62826] so im quite confused now..

so i dont know what to do and HOPE VERY MUCH someone will check my result v(2)=6,8;-15,7 and tell me if its right or not and if so what i can do to get the right result

Attached Thumbnails

 

NasuSama

Actually, your answer is correct if you refer angles with radians only. There seems to be no incorrect approach here.

What someone just did is to factor out 25 for each vector. Then, simplify the values. Yours and someone's answers are equivalent.

Nicely done!

mimi.janson

Oh GREAT !! this answer is the one that has made me most happy ever <3

:)