"A slinky that satisfies v = sqrt(T/_mu) is stretched 12m. The mass of the slinky is 0.8kg. The tension on the slinky is 4N. What is the expected wave speed?"
To get mu, I divided the mass by the length then plugged that into the equal and solved for v but I'm not getting the correct answer.
It sounds like you did it right.
mu is 0.8/12 = 0.0667 kg/m
T is 4 N.
I get v = 7.74 m/s
Use one significant figure (recommended) and you get 8 m/s.