Because the slope is 1: root number 3, the inclination angle is 30 degrees, so the angle ABC is 60 degrees. When the triangle PQB is a right triangle, its PB=2BQ, or 2PB=BQ.

If the condition is met after t seconds, there is 30-0.5t=2*0.5t, and the solution is t= 10 second.

Or 2(30-0.5t)=0.5t, t=20 seconds.

Therefore, PQB is a right triangle after 10 seconds or 20 seconds away.