SOLUTION: An object is thrown downward with an initial velocity of 7 feet per second. The relationship between the distance s it travels and time t is given by s=7t+16t^2. How long does it t

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: An object is thrown downward with an initial velocity of 7 feet per second. The relationship between the distance s it travels and time t is given by s=7t+16t^2. How long does it t      Log On


   

Question 1161261: An object is thrown downward with an initial velocity of 7 feet per second. The relationship between the distance s it travels and time t is given by s=7t+16t^2. How long does it take the object to fall 78 feet?
Found 2 solutions by math_helper, Boreal:
Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!


+16t%5E2+%2B+7t+=+78+



+16t%5E2+%2B+7t+-+78+=+0+

+%28t+-+2%29%2816t+%2B+39%29+=+0+

 

Solutions are:

 t = 2 

 t = -39/16    <<< discard, negative time is N/A



 +highlight%28t=2%29+ sec



Check:  s at t=2: 16(4) + 7(2) = 64 + 14 = 78  (ok)

Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
s=7t+16t^2=78
so 16t^2+7t-78=0
(16t+39)(t-2)=0
t=2 seconds.