Two ships are `10 km` apart on a line joining south to north. The one farther north is steaming west at `20 km h^-1`. The other is steaming north at `20 km h^-1`. What their distance of closest approach ? How long do they take to reach itb ?
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Explanation

Solving from the frame of particle 1,
we get `d_("short") = 10 cos 45^@`
=`(10)/(sqrt(2)) = 5 sqrt(2) km`
`t = (10 sin 45)/(|vec V_(21)|) = (10 xx 1//sqrt(2))/(20 sqrt(2))`
=`(1)/(4) h = 15 min`.
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