# Homework Help: Pendulum Problem?

1. Dec 3, 2008

### Kandycat

1. The problem statement, all variables and given/known data
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?

2. Relevant equations
umm... the only equation to find helpful was...

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

3. 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?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Dec 4, 2008

### alphysicist

Hi Kandycat,

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?

3. Dec 4, 2008

### 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!