# Acceleration and speed -- confused

mncyapntsi
Homework Statement:
Which of the following statements are false:

The speed at 2.1 min is less than at 2.6 min.
The acceleration is zero at 0.5 min and 4.2 min.
The acceleration is non-zero at 6.2 min.
The acceleration is never negative.
The acceleration is non-zero at 2.3 min.

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Relevant Equations:
a(t) = dv/dt; v(t) = dx/dt; ...
I've written in that only the first statement was False, however my classmates aren't getting the same answer?

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Can you explain why you think the rest are true?

mncyapntsi
Can you explain why you think the rest are true?
Here is my reasoning:

The acceleration is zero at 0.5 min and 4.2 min: true because x(t)=constant so v(t)=0 so a(t)=0

i just rethought this one - false right?: The acceleration is non-zero at 6.2 min: false because x(t)=mx+p so v(t)=constant so a(t)=0

The acceleration is never negative: true bc nowhere is v(t)<0

i just rethought this one - false? The acceleration is non-zero at 2.3 min: false because x(t)=mx+p so v(t)=constant so a(t)=0

PeroK
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The acceleration is never negative: true bc nowhere is v(t)<0
Negative acceleration means that the object is slowing down. Not that the velocity is negative.

mncyapntsi
mncyapntsi
Right! So only one of them is true - the second one?

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Right! So only one of them is true - the second one?
That's what I think.

mncyapntsi
mncyapntsi
Thanks for helping me think through that, and clearing it up!

PeroK