# Homework Help: Velocity of a projectile fired horizontally from a spring launcher ballistic pendulum

1. Feb 29, 2012

### lip1993

I am trying to determine the velocity of a ball fired horizontally from ballistic pendulum. The data is as follows:
ball mass: 62.2 g
spring mass: 14.7 g
rod mass: 89.3 g
length of spring: 126.1 mm
initial spring length: 5 cm
compressed spring length: 1 cm
k: 2.05 N/m calculated from previous experiment

Using the Work-Kinetic Energy Theorem
Kbo + Kro + Kso = Kb + Kr + Ks
.5mv^2oball + .5mv^2orod + .5kx^2 = .5mv^2ball + .5mv^2rod - .5kx^2
I took all the terms to 0 and got v_oball = (kx^2 /m_ball)^.5.

this doesn't seem correct, shouldn't the mass and lengths of the spring and rod be used?

2nd part is to determine the range it should travel from a height of 101.05 cm above ground fired horizontally.
I used the R = v^2 /g sin2t but since angle t= 0 I am getting 0 for the range.

Last edited: Feb 29, 2012
2. Mar 1, 2012

### tiny-tim

welcome to pf!

hi lip1993! welcome to pf!

(try using the X2 button just above the Reply box )
i don't understand the set-up

do you mean a ball fired horizontally at a ballistic pendulum (from a spring)?