SOLUTION: If an object is projected vertically upward from ground level with an initial velocity of 280 ft/sec, then its distance s above the ground after t seconds is given by s = −

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: If an object is projected vertically upward from ground level with an initial velocity of 280 ft/sec, then its distance s above the ground after t seconds is given by s = −      Log On


   



Question 950715: If an object is projected vertically upward from ground level with an initial velocity of 280 ft/sec, then its distance s above the ground after t seconds is given by
s = −14t2 + 280t.
For what values of t will the object be more than 1050 feet above the ground?

______ < t < ______

Found 2 solutions by MathLover1, josmiceli:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

s+=+-14t%5E2+%2B+280t
For what values of t will the object be more than 1050+feet above the ground?
1050+%3E+-14t%5E2+%2B+280t
14t%5E2-280t+%2B1050+%3E+0..............simplify, both sides divide by 14
t%5E2-20t+%2B75+%3E+0......factor completely
t%5E2-15t+-5t%2B75+%3E+0
%28t%5E2-15t%29+-%285t-75%29+%3E+0
t%28t-15%29+-5%28t-15%29+%3E+0
%28t-5%29+%28t-15%29%3E=0
solutions:
%28t-5%29%3E=0=>t%3E=5
%28t-15%29%3E=0=>t%3E=15
combined:
5%3Cx%3C15

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+s+%3E+1050+
+s+=+-14t%5E2+%2B+280t+
----------------------
Set +s+=+1050+ ft
+1050+=+-14t%5E2+%2B+280t+
+-14t%5E2+%2B+280t+-+1050+=+0+
+-7t%5E2+%2B+140t+-+525+=+0+
+-t%5E2+%2B+20t+-+75+=+0+
I notice that +75+=+15%2A5+, so I
can say:
+%28+-t+%2B+15+%29%2A%28+t+-+5+%29+=+0+
+-t+%2B+15+=+0+
+t+=+15+
and
+t+-+5+=+0+
+t+=+5+
-------------
+s+%3E+1050+ ft for
+t+%3E+5+ sec
+t+%3C+15+ sec
---------------
+5+%3C+t+%3C+15+ sec
------------------
Here's the plot:
+graph%28+400%2C+400%2C+-5%2C+25%2C+-300%2C+1500%2C+-14x%5E2+%2B+280x%2C+1050+%29+