# Energy and WET (Springs)

1. Oct 17, 2008

### closer

A toy cannon uses a spring to project a 5.30 g soft rubber ball. The spring is originally compressed by 5.00 cm and has a force constant of 9.00 N/m. When it is fired, the ball moves 16.0 cm through the horizontal barrel of the cannon, and a constant frictional force of 0.0320 N exists between barrel and ball.

(a) With what speed does the projectile leave the barrel of the cannon?

Wnet = $$\Delta$$KE
Ws - Wfk = .5mv2 - 0
.5kx2 - fkd = .5mv2
.5(9)(.052) - (.032)(.11) = .5(.0053)v2
v = 1.7079

Final answer is incorrect. Any ideas?

2. Oct 17, 2008

### krausr79

Have you tried replacing .11 with .16? Friction acts over full length of barrel. What is the answer?