A man walking at 3km/hr crosses a square field diagonally in 2 min. The area of the field is?

speed = 3 x ( 5/18 ) m/sec.
= 5 / 6 m/sec.
∴ Distance covered in 2 min. = ( 5 / 6) x 2 x 60 m
= 100 m.
∴ Length of diagonal = 100 m
Area of the field = 1/2 x diagonal²
=1/2 x 100 x 100 m²
= 5000 m²
= 50 acres.