- #1
jameslat
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Homework Statement
If a tennis ball with a mass of 57 g is shot out of a spring cannon at a 45 degree angle and goes 10m find the answer to the following questions:
What is the velocity.
What spring constant must the cannon have.
What would be the constant converted into lbs/in.
Homework Equations
FS=-kx
vf^2=vi^2 + 2ax
x=(vi^2(sin^2(theta)))/-a
F=ma
The Attempt at a Solution
ok i started off with finding the vi
10=vi^2(.5)/9.8
vi^2=100
vi=10
and with that then i can now try and find the acceleration of the spring right?
from 0 to 10m/sec
vf^2=vi^2+2ax
10^2=0+2ax
50=ax
50/x=a
first question is this x referring to x as how far i must pull back the string or the distance that i will be shooting at? (10 m)
f=ma
F=-kx
so
ma=-kx
.057(50/x)=-kx
2.85/x=-kx
2.85=-kx^2
good so far?
then at this point I am supposed to guess a K and use that.
so a 20 lbs/in has 2.2597 N/m
( http://www.boltscience.com/pages/convert.htm )
2.85/2.2587=x^2
so x = 1.12 m
so i would have to pull in back a meter?
if i set k to 31
2.85/31=x^2
x=.30 which is abt a foot right?
but 31 N/m is like almost 300 lbs/in spring!
what am i doing wrong?
Thanks for any input.
-James
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