Answer:
a = 5 or a = -5
Step-by-step explanation:
To Find :
Position vector at time
and
.
Solution :
r (t) = 2 (t −7)i + 12t j
Putting t = 5 s and t = 8 s, we get :
r(5) = 2( -2 )i + 60j
r(5) = -4i + 60j
r(8) = 2i + 96j
Now, to find speed differentiating the r(t) w.r.t t :

Hence, this is the required solution.