Finding acceleration in spring situations

[bunk66]

Homework Statement

A duck of mass 40kg is being pulled by a spring with k = 900N/m. If μ_k = 0.6 between the duck and the road, find the acceleration of the duck given that the spring stretches 0.4m.

Homework Equations

F_spring = kx, where k = spring constant and x = stretch of spring
F_net = ma

The Attempt at a Solution

F_spring = kx
F = 900N/m(0.6m)
F = 540N

That's about as far as I got before not knowing what to do next.

 

[haruspex]

F = 900N/m(0.4m)
F = 540N

Those are two different forces, so give them different names.
In which directions do they act?
How do they relate to the acceleration of the duck?

 

[bunk66]

Those are two different forces, so give them different names.
In which directions do they act?
How do they relate to the acceleration of the duck?

What exactly do you mean that they are two different forces? In the section that you quoted, isn't there only one force being calculated: the spring force?

And p.s, I made a typing error. Where it says 0.4, it should be 0.6

 

[haruspex]

I made a typing error. Where it says 0.4, it should be 0.6

OK, that's what made me think you were referring to two different forces.
So, what is the frictional force acting on the duck (direction and magnitude)?

 

[bunk66]

OK, that's what made me think you were referring to two different forces.
So, what is the frictional force acting on the duck (direction and magnitude)?

I mixed some of the numbers apparently.

Fspring = kx
F = 900N/m(0.4m)
F = 360N

40kg x 9.8 = 392N

F_f = μ_k(F_N)
F_f = 0.6(392N)
F_f = 236N

Fnet = Fa - Ff
Fnet = 360N - 236N
Fnet = 124N

Fnet = ma
Fnet/m = a
124N / 40kg = a
3.1 m/s2 = a

Evidently that was a lot easier than I made it out to be