# Homework Help: Spring Gun Question

1. Oct 25, 2007

### Oliviam12

1. The problem statement, all variables and given/known data

A spring-loaded toy dart gun fires darts with a mass of 104 g. When the spring in the dart gun is compressed 8 cm, the dart flies off with a speed of 11.4 m/s. What is the spring constant of the spring in the dart gun?

2. Relevant equations
W=1/2*k*x^2
V=sqrt(2W/m)

3. The attempt at a solution
Not really much of a clue on how to do this problem, I tried to use this example;

A spring with spring constant 218.5 N/m is compressed by 0.291 m. Then a steel ball bearing of mass 0.0733 kg is put on the spring, and the spring is released. What is the speed of the ball bearing right after release? (The ball bearing will come off the spring exactly as the spring returns to its equilibrium position. We will assume that we can neglect the mass of the spring in this calculation.) W = 1/2*k*x^2 then us this equation: v = sqrt(2W/m)

I found on Google and work backwards but, it got confusing and messy. I did find the
kinetic energy to equal 6.7 J, but I don't think I need it?

2. Oct 25, 2007

### Astronuc

Staff Emeritus
If one assumes conservation of energy and no losses due to friction (i.e. dissipative forces), then the energy stored in the spring become kinetic energy of the dart.

Equate the stored energy of the spring and the kinetic energy of the dart.

3. Oct 25, 2007

### Oliviam12

Thanks! That tip kind of caused an epiphany and I got it now.