Hello there!

Greetings!

Although you haven't completed your question but I guess the question is asking to find the time when the two velocities are at 90 degree.

Now , to solve the problem let ( 3, v1) be first velocity and (-4,v2) be second velocity

Then,

V1 = v2= get = 10t

(3,10t) * (-4,10t) =0

-12 + 100t^2 = 0

t = (0.12)^1/2s i.e root 0.12 s.


Thankyou