# Simple Pendulum Motion and Physical Pendulum

#### danield

1. The problem statement, all variables and given/known data
1) Find the period of a pendulum 50 cm long when it is suspended in (a) a stationary elevator; (b) an elevator falling at the constant speed of 5.0 m/s; (c) an elevator falling at the constant acceleration of 2.0 m/s2; (d) an elevator rising at the constant speed of 5.0 m/s; (e) an elevator rising at the constant acceleration of 2.0 m/s2.

2. Relevant equations
Period = 2 pi Squareroot of Length of arm/ Gravity

3. The attempt at a solution
1) I could solve a) by simply replacing data into the formula, but im not sure how does the change in velocity and acceleration affects the data that is where im stuck at.

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#### Pythagorean

Gold Member
A force has to be introduced to change the period.

Constant motion doesn't introduce force, only acceleration does.

#### danield

so that means that when the velocity is up or down 5m/s constat there is no acceleartion, so only G is taken into account???
but for the toher two, how are they calculated?

#### Pythagorean

Gold Member
Gravity is an acceleration... the period is actually

P = 2*pi*sqrt(L/a)

where a is acceleration.

Gravity is always there, but in acceleration situations a will not simply be equal to G as it is in the stationary and constant motion situation.

#### danield

Yes i understand that part, but what i don't know is how does the up and down acceleration influence the total acceleration, this is just a hunch but i think that when acceleration is downward i would be 7.81, and when it is upward it will be 11.81, im not totally sure about that
As for the ones where velocity is constant i think that the only acceleration acting is gravity, and im not sure of that either..

#### Doc Al

Mentor
You are correct. The acceleration of the elevator adds (or subtracts) from the standard acceleration due to gravity (9.81 m/s^2).

#### danield

ok thanks very much

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