# Simple harmonic motion (direction of acceleration)

1. Jun 9, 2014

### kelvin macks

1. The problem statement, all variables and given/known data
my question is on part d, (iv), i assume this is a pendulum experiment. the equlibrium position is at 30cm. then the negative amplitude should be located at 24.0cm. the particle moved from 24.0cm to 36.0cm. the acceleration is always acted towards the equlibrium position. so for d part(i) and (ii) should be positive since it's in the same direction with acceleration. But at 34.0cm, which is on the right of equlibrium position, (the particle travel form left to right), so the particles is moving away from equlibrium position, so the acceleration should be negative? am i right?
Because the motion is oppostite to the direction of acceleration (acceleration is towards the equlibrium position)..

please correct me if my concept is wrong. thank you!

2. Relevant equations

3. The attempt at a solution

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2. Jun 9, 2014

### rude man

You are right. The answer to (d) part 4 is wrong as indicated in your figure.

3. Jun 9, 2014

### BiGyElLoWhAt

One way to checit mathematically is to write your position function and take the derivative twice. Solve for your t values in the position function that give you the given platoon and given direction of velocity, then plug them into your acceleration function and you'll not only have the direction but the magnitude as well.