# Simple pendulum and harmonic motion

#### Jm4872

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

A simple pendulum is 5.20 m long. What is the period of simple harmonic motion for this pendulum if it is hanging in an elevator that is accelerating upward at 5.90 m/s2?

2. Relevant equations

T=2pi*(sqrt(L/g))

3. The attempt at a solution

all I did was plug in the value of the length of the pendulum into the equation like so:
T=2pi*(sqrt(5.2/9.8))=4.58s
but this answer is not right? I'm so confused as to what I am supposed to do and why I am given acceleration if I dont even need it.

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#### antibrane

If you know how to derive this equation you are using, I would go through it and look at where the gravitational acceleration, g, comes in. If the pendulum is feeling a vertical acceleration from the elevator now, in addition to the gravitational acceleration, how would that affect your derivation/equation?

#### cepheid

Staff Emeritus
Gold Member
You're not in a stationary frame of reference. You're in an accelerating frame of reference. Think about it. When you are in an elevator that is accelerating upward (e.g. when it first begins to move) do you feel lighter, heavier, or nothing at all?

It's almost as if a mysterious force has cropped up ;)

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