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EinsteinApple
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Homework Statement
Laura propels a stone straight up with her slingshot. The stone strikes a tree branch 4.0m above her. It strikes the branch with a velocity of 5.0m/s. How long does this take?
a= -9.81 m/s2
v1 = 5.0m/s
d= 4.0 m[/B]
Homework Equations
d=vit+1/2at2[/B]
d=v1+v2/2 x t
v2=v1+at
The Attempt at a Solution
ATTEMPT 1: DOESN'T WORK
I believe I should use d=vit+1/2at2
therefore:
4m = (5.0)(t)+1/2(-9.81)(t)2
-4.91t2 + 5.0t -4 =0
However I can't do this because using quadratic I get a negative. Therefore it's not an option.
ATTEMPT 2: CAN I ASSUME v2=0?
d=v1+v2/2 x t
4=(5)+ (0)/2 x t
t = 1.6s
* But I guess I can't assume the V2=0
Attempt 3: CAN I ASSUME v2=0?
v2=v1+at
0=5 +(-9.81)t
t = 0.51 s.
I know the answer is 0.53s, however how do I know whether I should use attempt 2 or attempt 3?
I know to use attempt 3 because it's the right answer, but in my mind 1.6 s makes sense too.
Please help!