# Acceleration and Velocity

1. Aug 9, 2008

### joe215

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

1. If an object has zero velocity, is its acceleration necessarily zero at that instant?

2. A book is moved around the perimeter of a table that is 1m x 2m. If the book ends up at its initial position, what is its displacement?

3. Can the sign of acceleration be positive for an object slowing down?

3. The attempt at a solution

1. No. Aan object could be accelerating from a negative velocity through a point of zero velocity. Therefore its acceleration is not zero, because it is speeding up.

2. Displacement is change in position, so the book's displacement is zero.

3. Yes, the sign of acceleration can be positive for an object that is slowing down. When an objects velocity and acceleration are in opposite directions, its speed decreases with time. An object with a negative velocity will slow down with a positive acceleration.

Are my explanations complete?

Thanks for any help!

Last edited: Aug 9, 2008
2. Aug 9, 2008

### nicksauce

Looks good to me.