# Homework Help: True or false velocity physics question double check

1. Jan 23, 2008

### Melchior25

So I just want to make sure I have the correct answers before I submit my question. So could anyone please just double check my answers?

Thanks

An object moves in one dimension along the x-axis. At some instant in time, the object is located at x = 5.2 m, is motionless, and has an instantaneous acceleration of -2.3 m/s2. What must be true about this object at this instant in time? (Select all that apply.)
The first derivative of a position vs. time graph at this point is zero. False
The second derivative of a position vs. time graph at this point is zero. True
The slope of a velocity vs. time graph at this point is positive. False
The slope of a velocity vs. time graph at this point is negative. True
The object is just about to start moving backwards. True
The object is just about to start moving forwards. False

Again, I just want to make sure these are right. I'm not sure if I am completely correct.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 23, 2008

### Leong

1. True. Because motionless means not moving means velocity is zero means first derivative of position towards time (ie velocity) is zero.

3. Jan 23, 2008

### Leong

2. False. The second derivative of position towards time means acceleration. at this point, the acceleration is not zero because it is given to you as -2.3 m/s^2.

4. Jan 23, 2008

### Melchior25

Thanks, Leong. I was actually a bit unsure about the first two. I wrote the equations out but some how had a feeling that I wasn't doing something right.