SOLUTION: For questions one and two use formula: s=-16t^2+vt+h 1) A rock is dropped from the top of an embankment into water that is 256 ft. A. in how many seconds will the rock hit the

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Question 515482: For questions one and two use formula: s=-16t^2+vt+h
1) A rock is dropped from the top of an embankment into water that is 256 ft.
A. in how many seconds will the rock hit the water
B. how long will it take before the rock is 112 feet above the water?
2) An object is thrown vertically downward with an initial velocity of 30ft/s from a point 200ft above the ground. find to the nearest second, the time needed for it to reach the ground
Answer by lwsshak3(11628) (Show Source):
You can put this solution on YOUR website!
For questions one and two use formula: s=-16t^2+
+h
1) A rock is dropped from the top of an embankment into water that is 256 ft.
A. in how many seconds will the rock hit the water
B. how long will it take before the rock is 112 feet above the water?
2) An object is thrown vertically downward with an initial velocity of 30ft/s from a point 200ft above the ground. find to the nearest second, the time needed for it to reach the ground
**
1) s=-16t^2+vt+h
assume initial velocity,v=0
h=256
s=-16t^2+256=distance rock is above the water t seconds after being dropped
A. 0=-16t^2+256
16t^2=256
t^2=256/16=16
t=√16=4 seconds
ans: The rock will hit the water after 4 seconds
..
B. 112=-16t^2+256
16t^2=256-112=144
t^2=144/16=9
t=√9=3 seconds
ans: The rock will be 112 feet above the water after 3 swconds
..
2) initial velocity=-30 ft/sec
h=200 ft
object 0 ft above ground
-16t^2-30t+200=0
16t^2+30t-200=0
8t^2+15t-100=0
use following quadratic formula to solve:
..

..
a=8, b=15, c=-100
t=[-15)�√((15)^2-4*8*(-100))]/2*8
t=[-15�√(225+3200)]/16
t=[-15�√3425]/16
t=(-15�58.52)/16
t=2.72
or
t=-4.6 (reject, time>0)
ans:
It will take 2.72 seconds for object to reach the ground