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Question 446162: oky so im practicig for the cst by using the cst release qestion but im havng trouble with worproblems and I've managed to solve some so far but therese that is !?!?
An object that is projected straight downward with initial velocity "v" feet per second travels a distance "s=vt+16t^2 ", where t=time in seconds. If Ramón is standing on a balcony 84 feet above the ground and throws a penny straight down with an initial velocity of 10 feet per second, in how many seconds will it reach the ground?
A 2 seconds
B 3 seconds
C 6 seconds
D 8 seconds
I've tried using the formula v=d/t like in science but this equation confuses me: s=vt+16t^2
Answer by mananth(12270)   (Show Source):
You can put this solution on YOUR website!s=vt+16t^2
v= 10ft/s
s=84
84=10t+16t^2
16t^2+10t-84=0
/2
8t^2+5t-42=0
Find the roots of the equation by quadratic formula Find the roots of the equation by quadratic formula
a= 8, b= 5, c= -42,
b^2-4ac=25-1344
b^2-4ac=1369
 =37
x1=(-5+37)/16
x1= 2
x2=(-5-37) /16
x2= -2.63
Ignore negative value
x = 2 seconds
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