Asked by mssailormouth

A toy "spring gun" has a spring with a spring constant of 30,000 N/m and is depressed 4 cm. It shoots a plastic dart with a mass of 45 grams. How fast will the dart travel if there is no friction?
Answered by oobleck
well, the KE of the dart will equal the PE stored in the spring, right?
Answered by mssailormouth
I'm not really grasping this concept well. I don't know if the KE of the dart is equal is the PE stored? Based on the formulas I don't know that is correct.

PE= 1/2kx^2
k=30,000
x=4cm

KE= 1/2mv^2
m=45g
v=0??
Answered by R_scott
where else is the stored spring energy going?

the problem says no friction
Answered by oobleck
KE = PE
1/2 mv^2 = 1/2 kx^2
Since k is in N/m, we need to use MKS units.
1/2 * 0.045 * v^2 = 1/2 * 30000 * 0.04^2
v = 32.7 m/s
Answered by mssailormouth
ooooh for some reason I thought I needed to subtract PE and KE and it wasn't making any sense.
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