# Homework Help: Vectors pendulum problem

1. Oct 31, 2008

### ScullyX51

1. The problem statement, all variables and given/known data
To understand that the direction of acceleration is in the direction of the change of the velocity, which is unrelated to the direction of the velocity.
The pendulum shown makes a full swing from -pi/4 to + pi/4. Ignore friction and assume that the string is massless. The eight labeled arrows represent directions to be referred to when answering the following questions.
What is the direction of vector A when the pendulum is at position 1?
What is the direction of vector A at the moment the pendulum passes position 2?What is the direction of vector A when the pendulum reaches position 3?

2. Relevant equations
I have no idea what equations I should be using here...I am very stuck and could use some hints to steer me in the right direction.

3. The attempt at a solution
All I know so far is that the acceleration is equal to the instantaneous rate of change in velocity.

File size:
10.7 KB
Views:
278
2. Nov 1, 2008

### tiny-tim

Hi ScullyX51!
I'm really confused …

is "vector A" the A in the picture, or is it the acceleration?

3. Nov 1, 2008

### ScullyX51

yes. I was very confused by that as well...but I am pretty sure vector a is referring to acceleration.

4. Nov 1, 2008

### tiny-tim

ok … then the question is asking where the acceleration is when something moves in a circle.

You can work this out using r and θ, or i and j, or just by drawing a little triangle where two sides are the velocities at angles θ and θ + dθ, and the third side is the change in velocity.

5. Nov 1, 2008

Thank you!