Answers

2014-06-01T18:00:48+05:30
Let velocity of man V1 = 10i
velocity of rain drop Vo = ai + bj
consider vertically downward direction as positive.
Vo1 = ai + bj - 10i
       = (a-10)i + bj 
raindrops appears to fall in vertical direction . hence X - component is zero 
  a-10 = 0
a = 10
in second case 
V2 = 20i
Vo2 = 10i + bj - 20i
       = -10i + bj
raindrops appears to fall in the direction making an angle 30 with vertical 
tan 120 = -10 / b    (angle is measured from positive X-axis  90 + 30 = 120)
-√3 = -10/b
b = 10/√3
hence velocity of raindrops w.r.t. ground Vo = 10i + 10j/√3
speed of raindrops w.r.t. ground = √{10² + (10/√3)²}
                           = √(100+100/3)
                            = 20/√3
direction tanα = (10/√3)/10
                      = 1/√3
 α = 30  w.r.t. ground.
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