- #1
EcKoh
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Homework Statement
Romeo is chucking pebbles as gently as he can up to Juliet's window. That is, he wants the pebbles to hit the wendow with the least possible speed. He is standing at the edge of a rose garden at Dv = 7.90 m below her window and at Dh = 8.50 m from the base of the wall. How fast are the pebbles going when they hit her window?
Homework Equations
Vf = Vi + adv (to find initial velocity)
Vf = Vi + at (to find hang time)
Dh = Vht (to find constant horizontal velocity)
The Attempt at a Solution
Okay so I'm assuming I did everything right, so I'm not sure where I went wrong but here are the steps I took in my attempt:
3.1: List knowns and unknowns:
Knowns:
Vf = 0 m/s
a = -9.8 m/s2
Dv = 7.90 m
DH = 8.50 m
Unknowns:
Vi = ?
3.2: Find the initial velocity:
Vf = Vi + adv
(0) = Vi + (-9.8)(7.90)
Vi = 77.42
3.3: Find hang time:
Vf = Vi + at
(0) = (77.42) + (-9.8)t
-77.42 = -9.8t
t = 7.9s <-- (maybe I went wrong here? I noticed that's the same as Dv
3.4: Find constant velocity:
Dh = Vht
(8.50) = Vh(7.9)
Vh = 1.08
So 1.08 m/s turns out to be the wrong answer, and I keep going back and reworking it but I'm not sure what I'm doing wrong. Its due online tonight in just a few hours, but either way it's driving me crazy so I just want to know what I'm doing wrong and how to fix it.
Thanks!