Question

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?

Answer 1

well, the KE of the dart will equal the PE stored in the spring, right?

Answer 2

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??

Answer 3

where else is the stored spring energy going?

the problem says no friction

Answer 4

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

Answer 5

ooooh for some reason I thought I needed to subtract PE and KE and it wasn't making any sense.