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I really need help with these questions

  1. Jun 18, 2013 #1
    I really need help with these questions...!!

    Question 1.
    Two balls A and b are thrown with same velocity u from the top of a tower.Ball A is thrown vertically upwards and B is thrown vertically downwards.
    If time of A=6s and B=2s..Find height of tower.

    Question 2.
    A boat having speed of 5km/hr in still water, crosses a river of width 1km along the shortest possible path in 15 minutes.Find the speed of the river in km/hr.


    I've tried everything but the answers are just not coming out right..
    pl help...
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 18, 2013 #2
    I'll give you some hints that should be useful - then you should try working the problems.


    First, you need to be careful when writing out the questions. In question one you say that both balls are thrown with the "same velocity" but then contradict yourself and say that one is thrown upwards and the other downwards - you should say they are thrown with the same speed.


    1. You will need to use one the basic kinematics formulas to solve this question. You will have two equations - one for ball A and one for ball B and you should be able to use these to solve for the height of the tower. (Hint: You may need to use substitution or elimination.)


    2. If you were to row a boat across a river in stationary water what would the shortest possible distance be?
     
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