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September 9th, 2018, 12:16 AM  #1 
Member Joined: Aug 2018 From: Nigeria Posts: 48 Thanks: 2  Dynamics; Kinematics (further math)
Hello guys, it's been long since I posted here due to the fact that I'm learning....I just want to present some question to this forum today... which consist of 1. Dynamics 2. Vector 3. Trigonometry I have no idea on both dynamics and vector... Believe me. I just want the mathematicians of this forum to solve for me. I would be grateful and the question I'll post today must consist of diagrammatic representation (pardon me, but it is compulsory).... Dynamics.... The speed of a boat in still water is 5m/s. The boat heads straight across a river which is 300m wide but actually travels at an angle of 60 degree to the bank (a) Calculate and correct to 2 d.p. 1. The speed of the boat relative to the ground 2. The speed of the current (b) what is the time taken by the boat to cross the river? Guys, please I have 0% knowledge of dynamics, therefore hints are not useful... you can even send attached pics solution. I would be grateful. Last edited by skipjack; September 9th, 2018 at 05:18 AM. 
September 9th, 2018, 01:45 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,887 Thanks: 1836 
The boat's rate of progress across the river isn't affected by the speed of the current, so the time the boat takes to cross the river is 300/5 seconds = 60 seconds. Let c m be the distance downstream that the boat is taken by the current. River.PNG By Pythagoras, c² + 300² = (2c)², so c = 100√3. Hence the speed of the current is c/60 m/s = 2.89 m/s to 2 d.p. The speed of the boat relative to the ground is 2c/60 m/s = 5.77 m/s to 2 d.p. 

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dynamics, dynamicskinematicsfurther, kinematics, math 
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