University physics, waves, multiple choice.

[thinktoohard]

Homework Statement

A cord with a mass of 40g is tied between two supports with a tension of 19.2N. The natural frequency of the cord is 10Hz. Find the length of the cord

a.1.2m b.2m c.289m d.34cm

Using your answer from Question 3, how long does the wave take to travel from one end of the string to the other?

a.0.1s b.0.05s c.50s d.20s

Homework Equations

v=squrt(forcetension/(mass/length))
v=wavelength/Period=wavelength*frequency

The Attempt at a Solution

Knowns:
fixed ends, string.
mass = 0.040 kg
Force Tension = 19.2N
Natural Frequency = 10Hz
length of the cord = ?

Calculated:
Period = 0.1 s
Weight = 0.392 N

Other stuff:
Velocity = ?
Wavelength = 2L = ?

I've basically just stared at it and played around with everything I can think of which gets me no where close to an answer, for the past hour trying to figure out what to do, Made an account just to ask this forum about it.

 

[TSny]

Hello, thinktoohard. Welcome to PF!

You need to show some attempt at a solution to receive help here.

You've got two "relevant equations" and one "other stuff equation" λ = 2L.

Show us your attempt at combining those equations to get a single equation for L in terms of the given quantities.

 

[thinktoohard]

Thanks anyways I figured it out, Sub λ = 2L -> f = v/λ -> L = v/(2f), -> sub into v = sqrt.(ft/(m/L)) for -> v = sqrt.(FT/(m/(v/2f))) then isolate for v, gives you v = 24.25 m/s, -> v/2f = L -> L = 1.2125 -> L/v = 0.05 s.