Saurabh Singh
Last Activity: 11 Years ago
at time t hours after 1:30
first person will be (7.5+5t) from O
second person will be (5t) from O
distance between two will be
(7.5+5t)^2 +(5t)^2
we need to minimize this
the plot would look like -->

so they are closest at 0.75 hours before 1:30
i.e 45 minutes before 1:30
i.e 12:45
Thanks & Regards
Saurabh Singh,
askIITians Faculty
B.Tech.
IIT Kanpur