By looking at the position versus time graph shown above, determine the following at each of the eight numbered instants of time:

A.) Is the object's position positive or negative?

B.) Is the object's velocity positive or negative?

C.) Is the object's acceleration positive or negative?

D.) Is the object speeding up (accelerating) or slowing down (decelerating)?

Solution

System, Interactions and Model: This exercise is a review of the definitions of position, velocity and acceleration. These concepts are used in several of the models in the hierarchy.

Answers:

3 Comments

  1. Anonymous

    The comment is very important.  Can you make a question that's part B to force them to determine if

    "In general, a body with negaive acceleration will have negative velocity."  is true.

    Then point our a car stopping/slowing is a counter example.

  2. Anonymous

    I believe the answer is partially wrong. Whenever acceleration is positive "", it accelerates "A", and whenever acceleration is negative "" it decelerates "D". But the table has occasionally "D" under "", and "A" under "".

  3. Anonymous

    You haven't understood the concept of accelerating or decelerating. An object is said to be accelerating when its Speed is increasing with time, it may have negative acceleration as that means that its velocity is becoming more negative, while deceleration means that its Speed  is decreasing with time that is it is approaching zero. 

    Hope it Helps (smile)