Solve Pendulum Problem: Tension 150 N, Mass .65 kg, 28m Apart

[Kandycat]

Homework Statement

A cord of mass .65 kg is stretched between two supports 28 m apart. If the tension in the cord is 150 N, how long will it take a pulse to travel from one support to the other?

Homework Equations

umm... the only equation to find helpful was...

T = 2pi$$\sqrt{m/(mg/L)}$$ = 2pi$$\sqrt{m/(F/L)}$$?

The Attempt at a Solution

Knowns:

F (tension) = 150 N
m = .65 kg
L = 28 m

2pi$$\sqrt{.65 kg/(150 N/28 m)}$$ = 2.19 s?

Though the book says it is 35 s...

Help? Should there be another equation that I should be using or did I miss something?

 

[alphysicist]

Hi Kandycat,

Homework Statement

A cord of mass .65 kg is stretched between two supports 28 m apart. If the tension in the cord is 150 N, how long will it take a pulse to travel from one support to the other?

Homework Equations

umm... the only equation to find helpful was...

T = 2pi$$\sqrt{m/(mg/L)}$$ = 2pi$$\sqrt{m/(F/L)}$$?

This is not a pendulum, so these equations do not apply here. In this problem, a cord is stretched and a pulse is made to travel along the cord, so you want to find an expression for the wave speed of a stretched string. What would that be?

 

[Kandycat]

Oh... so is it v = $$\sqrt{F(t)/(m/L)}$$?

v = $$\sqrt{150 N/(.65 kg/ 28 m)}$$ = 80.35 m/s

T = L/v = 28 m/80.35 m/s = .35 s

Thanks!

Sorry about that.

 

[alphysicist]

That looks right to me!