SOLUTION: Help please! I'm so confused by this problem...
if an object is thrown vertically upward with an initial velocity of v, from an original position of s, the height h at any time
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Question 763757: Help please! I'm so confused by this problem...
if an object is thrown vertically upward with an initial velocity of v, from an original position of s, the height h at any time t is given by: h=-16t^2+vt+s
(where h and s are in ft, t is in seconds and v is in ft/sec)
a package is thrown downward with an initial velocity of -5ft/sec from a helicopter at 300 ft.
a) what is the height of the package in 2 sec?
b) how long does it take to hit the ground?
Found 2 solutions by solver91311, rothauserc:
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
\ =\ -16t^2\ +\ v_ot\ +\ h_o)
For 
ft/sec and 
feet
\ =\ -16t^2\ -\ 5t\ +\ 300)
Then for 
seconds
\ =\ -16(2)^2\ -\ 5(2)\ +\ 300)
Do the arithmetic
The ground is 
so:
Solve the quadratic for 
.
Discard the negative root.
John
Egw to Beta kai to Sigma
My calculator said it, I believe it, that settles it
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
f an object is thrown vertically upward with an initial velocity of v, from an original position of s, the height h at any time t is given by: h=-16t^2+vt+s
(where h and s are in ft, t is in seconds and v is in ft/sec)
=============================================================================
note that an object thrown upward would have a positive value for the initial velocity (v)....in our case the object is thrown downward so the value for v is negative.
==============================================================================
a) what is height after 2 seconds?
h = -16*t^2 +v*t + s
h = -16*(2^2) -5*2 + 300
h = -64 -10 +300
h = 226 feet after 2 seconds
=============================================================================
b) how long does it take to hit the ground? that is h=0
0 = -16t^2 -5t + 300
divide by -1 and we get
0 = 16t^2 +5 - 300
use quadratic formula
t = (-5+sqrt(25-4*16*-300)) / 32 = 4.18
t = (-5-sqrt(25-4*16*-300)) / 32 = -4.49
t reaches the ground in 4.18 seconds
============================================================================
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