SOLUTION: A rocket is launched from atop a 73-foot cliff with an initial velocity of 142 ft/s. The height of the rocket above the ground at time t is given by h=-16t^2+142t+73. A) When wi

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Question 1155173: A rocket is launched from atop a 73-foot cliff with an initial velocity of 142 ft/s. The height of the rocket above the ground at time t is given by h=-16t^2+142t+73.
A) When will the rocket hit the ground after it is launched? Round to the nearest tenth of a second.(Solve Algebraically, Hint: Use the Quadratic Formula to solve and the round the square root answer one decimal place)
B) When will the rocket reach 199ft from the ground? (Solve Algebraically)

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A rocket is launched from atop a 73-foot cliff with an initial velocity of 142 ft/s.
The height of the rocket above the ground at time t is given by h=-16t^2+142t+73.
:
A) When will the rocket hit the ground after it is launched? Round to the nearest tenth of a second.(Solve Algebraically, Hint: Use the Quadratic Formula to solve and the round the square root answer one decimal place)
h = 0 when it hits the ground
-16t^2 + 142t + 73 = 0
The quadratic formula: x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a=-16, b=142, c=73
t+=+%28-142+%2B-+sqrt%28142%5E2-4%2A-16%2A73+%29%29%2F%282%2A-16%29+
:
t+=+%28-142+%2B-+sqrt%2820164%2B4672+%29%29%2F%28-32%29+
:
t+=+%28-142+-+sqrt%2824836%29%29%2F-32+%29%29+, the positive solution
do the math
t = 9.3623 ~ 9.4 seconds
:
B) When will the rocket reach 199ft from the ground? (Solve Algebraically)
-16t^2 + 142t + 73 = 199
-16t^2 + 142t + 73 - 199 = 0
-16t^2 + 142t - 126 = 0
a=-16; b=-142, c=-126
t+=+%28-142+%2B-+sqrt%28142%5E2-4%2A-16%2A-126+%29%29%2F%282%2A-16%29+
:
t+=+%28-142+%2B-+sqrt%2820164-8064+%29%29%2F%28-32%29+
:
t+=+%28-142+-+sqrt%2812100%29%29%2F%28-32%29+
do the math
t = 7.875 ~ 7.9 seconds reaches 199 ft the 2nd time
and
t+=+%28-142+%2B+sqrt%2812100%29%29%2F%28-32%29+
t = 1 second reaches 199 ft the first time