Maths-
General
Easy
Question
Two cars A and B are moving uniformly on two straight roads at right angles to one another at 40 and 20 km/hr respectively. A passes the intersection of the road when B has still to move 50 km to reach it. The shortest distance between the two cars and the time when they are closest are
minutes
- 20 km, 10 minutes
- 20 km, 20 minutes
- None of these
The correct answer is:
minutes
Let the two be closest after time t, their initial position are O for A and B such that OB = 50. If they are now at
and
respectively, then


If
is least then
is also least.
\ 
Þ 
Þ
minutes
Clearly 
\ z is least
Putting
we get z = 202+ 402 = 202×5 = 
\

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