SOLUTION: Could you help me solve this problem ? An object is thrown downward with an initial velocity of 4 ft/s. The relationship between the distance (d) it travels and time (t) in sec

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Question 1041931: Could you help me solve this problem ?
An object is thrown downward with an initial velocity of 4 ft/s. The relationship between the distance (d) it travels and time (t) in seconds is given by : d=4t%2B15t%5E2
How long does it take the object to fall 135 feet ?
Write a complete sentence answer..
Thank you so much !!!
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The instant that the object is thrown down must
be +t+=+0+, and the object hasn't moved any distance
yet, so it must be true that:
+0+=+4t+%2B+15t%5E2+ , and it is if +t+=+0+
When the object has travelled +135+ ft,
then it must be true that
+d+=+135+
+135+=+4t+%2B+15t%5E2+
------------------------
+15t%5E2+%2B+4t+-+135+=+0+
Use quadratic formula
+t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
+a+=+15+
+b+=+4+
+c+=+-135+
+t+=+%28-4+%2B-+sqrt%28+4%5E2-4%2A15%2A%28-135%29+%29%29%2F%282%2A15%29+
+t+=+%28-4+%2B-+sqrt%28+16+%2B+8100+%29%29+%2F+30+
+t+=+%28-4+%2B-+sqrt%28+8116+%29%29+%2F+30+
+t+=+%28-4+%2B+90.09+%29+%2F+30+
+t+=+86.09+%2F+30+
+t+=+2.87+
It takes 2.87 sec to fall 135 ft
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I'm not sure what is meant by " answer in complete sentence "