- #1
MissJewels
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Homework Statement
A stone is thrown from a cliff 100 meters high with an initial velocity v0 = 25 m / s and at an angle of 53° projection from the horizontal axis. determine:
a) the time before it reaches the ground
b) the maximum height
c) its horizontal reach
d) its speed when it hits the ground
Homework Equations
I selected these:
vx0 = v0cos(53)
vy0 = v0sin(53)
Then I applied these t the following equations:
xf= vx0t
yf= y0 + vy0t+ (1/2)(-9,8)t2
t= ( -b± √(b2 - 4ac) ) / 2a
The Attempt at a Solution
So, for part a), using the above equations I found:
vx0 = v0cos(53)
vx0 = 25cos(53) = -22,96
xf= vx0t
xf= -22,96t
vy0 = v0sin(53)
vy0 = 25sin(53) = 9,898
yf= y0 + vy0t+ (1/2)(-9,8)t2
0= 100 + 9,898t+ (1/2)(-9,8)t2
Then, with that last equation, I used this equation: t= ( -b± √(b2 - 4ac) ) / 2a
to find t= -3,62s
When the answer SHOULD BE 7s... What am i doing wrong?
then, i tried b) using vf= 0
using the equation(H is maxheight):
vf2 = v0 -2(9,8)(H-100)
0 = 252 -16,9H +1690
H = 136,98 m
And the right answer should be 120m... GRR !
As for c), I don'T quite understand how to measure it... do i find xf?
d) Its supposed to be (15i -48,6j) m/s but i forgot how to calculate vectors.
ANYWAY PLEASE HELP! Its easy for you, but for me, this is hard. ;(