A man on the top of a rock rising on seashore observes a boat coming towards it.If it takes 20 minutes for the angle of depression to change from 30deg to 60deg ,how soon the boat reach the shore?
A)15 min
B)10 min
C)12 min
D)18min

• B 10minutes
• 9 years agoHelpfull: Yes(2) No(0)
• D| ' - _
  | ' - _
  | ' - _
  | ' - _
  h| ' - _
  | ' - _
  |____60______________30____';
  A BC
  
  
  Let AC is 60km or meter any thing
  
  so tan30 = h/ 60
  => 1/root3=h/60
  => h=60/root3 -----------------(1)
  
  tan 60 =h/x
  => root3 = h/x
  => h= root3 * x ----------------(2)
  
  compare both
  
  root3 * x = 60/ root3
  => x= 60 /(root3*root3)
  => x= 60/3
  => x= 20
  
  so 60-20= 40
  
  if ship take 20 min to cover 40 so it take 10 min to cover 20 ... (Y)
  
  I hope it is better explaination ,,,.. :)
  
  
• 8 years agoHelpfull: Yes(1) No(0)