SOLUTION: Benjamin threw a rock straight up from a cliff that was 48 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=-16t^2+52t+48, how m

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Question 1035819: Benjamin threw a rock straight up from a cliff that was 48 ft above the water. If the height of the rock h, in feet, after t seconds is given by the equation h=-16t^2+52t+48, how many seconds will it take for the rock to hit the water?
Found 2 solutions by josmiceli, ikleyn:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The rock hits the water when +h+=+0+
+h+=+-16t%5E2+%2B+52t+%2B+48+
+0+=+-16t%5E2+%2B+52t+%2B+48+
Divide both sides by +4+
+-4t%5E2+%2B+13t+%2B+12+=+0+
Use quadratic formula
+t+=+%28+-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+-4+
+b+=+13+
+c+=+12+
-------------
+t+=+%28+-13+%2B-+sqrt%28+13%5E2+-+4%2A%28-4%29%2A12+%29%29+%2F+%282%2A%28-4%29%29+
+t+=+%28+-13+%2B-+sqrt%28+169+%2B+192+%29%29+%2F+%28-8%29+
+t+=+%28+-13+%2B-+sqrt%28+361+%29%29+%2F+%28-8%29+
+t+=+%28+-13+-+19+%29+%2F+%28-8%29+
+t+=+%28+-32+%29+%2F+%28-8+%29+
+t+=+4+
Note that I had to use the negative square root of +361+
so that +t+ came out to be positive
-------------------
The rock takes 4 sec to hit the water
--------------------------------
Here's the plot:
+graph%28+400%2C+400%2C+-2%2C+6%2C+-10%2C+100%2C+-16x%5E2+%2B+52x+%2B+48+%29+

Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
.
Benjamin threw a rock straight up from a cliff that was 48 ft above the water. If the height of the rock h, in feet,
after t seconds is given by the equation h=-16t^2+52t+48, how many seconds will it take for the rock to hit the water?
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