Direct intervals

Question

If w varies directly with j and inversely with the square of u and w=-5 when j=2 and u =0.5 find j if w=72 and u =6

Answer 1

Hi Tamika

 

Let's write the two initial conditions that "w" has to satisfy:

 

First, "w" varies directly with "j" and inversely with u². It means, that: w = A*j/u²  where A is any real number

 

 

We know that  w = -5 when  j=2 and  u=0.5 (or. u = 1/2)  It means:   -5 = A*2/(0.5)²  or   -5  = A*8

 

Right now, we have found the value of A = -5/8

 

Now, we need to find "j" if w=72 and u=6.  The solution is:   w = (-5/8)*j/u²  Evaluating this expression for w=72 and u=6 we have: 72 = (-5/8)*j/(6)².  If you leave "j" in one side, you have:   

 

j = 72*36/(-5/8)    (Tamika, you have to check if the value of w=72 is correct. It looks very big for me)

 

Nicolas Martin

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