Q. 5 C4.4( 7 Votes )

Attempt any two s

Answer :


Let O be the starting point.


A walks towards North with 4 km/h and B walks towards East at 8 km/h after 1 hour.


Let A reaches point A and B reaches point B when they are 20 km apart.


Let the travel time of B = x hours


Travel time of A = (x + 1) hours


OA = speed × time = 4(x + 1) km


OB = 8x km


Now by Pythagoras theorem,


AB2 = OA2 + OB2


202 = [4(x + 1)]2 + (8x)2


400 = 16(x2 + 1 + 2x) + 64x2


25 = x2 + 2x + 1 + 4x2


5x2+ 2x – 24 = 0


5x2 – 10x + 12x – 24 = 0


5x(x – 2) + 12(x – 2) = 0


(x – 2) (5x + 12) = 0


x = 2 or x = -12/5


travel time of B = x hours = 2hours


Travel time of A = (x + 1) hours = 2 + 1 hours = 3 hours


Hence, at 10:00 am they will be 20 km apart.


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