# Multiple choice question about constant velocity

1. Jan 21, 2014

### Tiven white

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

Which of the following is NOT true about an object having constant velocity?
Select one:
a. It has constant speed
b. It is moving in a steady/fixed direction
c. It has constant acceleration
d. It might be at rest
e. It might have a fixed position

2. Relevant equations

3. The attempt at a solution just need a little verification i say the answer is 'a' since velocity is a vector and is dependent on direction/displacement not speed any help will be appreciated

2. Jan 21, 2014

### Staff: Mentor

Velocity is speed and direction. If speed is zero, the direction doesn't matter. If acceleration and speed are both zero, I don't see which answer is better than the others... Is that really the whole problem statement?

3. Jan 21, 2014

### Tiven white

yes sir that is infact the entire question

4. Jan 21, 2014

### Staff: Mentor

I've asked for other Homework Helpers to check this, and so far the opinion is that the question is incorrect. Can you please check this with your instructor?

5. Jan 22, 2014

### tiny-tim

Hi Tiven white! Welcome to PF!
I'd go with b …

if its velocity is zero, then its velocity is constant, but it's not moving.

6. Jan 22, 2014

### D H

Staff Emeritus
Given the target audience, I'd go with e, where (e) means one or more of none of the above, not enough information, or this is a stupid question.

Options a, d, and e are easily eliminated. (Tiven white: Why did you think option a is the right answer? Constant velocity necessarily implies constant speed.)

That leaves options b and c as the only possible solutions. Choosing between them? A constant velocity necessarily implies zero acceleration, and zero is obviously constant. On the other hand, an object with a constant velocity of zero is steadily moving nowhere.

7. Jan 22, 2014

### tiny-tim

"moving nowhere" … in ordinary english, that's not moving!

(or does it mean infinitely fast? … it reminds me of those drivers who say "the car that i hit came from nowhere!" )

8. Jan 22, 2014

### D H

Staff Emeritus
And in ordinary English, constant velocity means not accelerating, which in ordinary English is not constant acceleration.

Interpreting ordinary English into mathematics is always suspect. This is a bad question.

9. Jan 22, 2014

### ViperSRT3g

If its got a constant velocity, it is neither changing speed or direction.

Thus, it has a constant speed (A).
If it is neither changing speed or direction, it must be moving in a steady or fixed direction (B).
The object may even be a stationary object, meaning it might be at rest (D).
This would imply a fixed position (E).

Therefore this object would NOT ever have a constant acceleration. So the answer (at least in my mind) is C, an object with a constant velocity would NOT have a constant acceleration.

10. Jan 22, 2014

### D H

Staff Emeritus
It's acceleration is zero. Is zero not a constant?

11. Jan 22, 2014

### ViperSRT3g

In terms of this question, I don't believe it was concerned about zero values. But yes, a constant acceleration of zero would exist. It is a poorly stated question, but I do feel that it implied a constant acceleration as acceleration that would actively alter the velocity of the object.

12. Jan 22, 2014

### Staff: Mentor

If the object is at rest, can we say "it is moving in a fixed direction"?

13. Jan 22, 2014

### D H

Staff Emeritus
We can say it's steadily moving nowhere.

Both (b) and (c) can be viewed as being true statements (and hence neither is the answer) or as false statements (and hence one or both is the answer). It's all in how one interprets those words. The problem certainly did open itself to zero velocity via options (d) and (e).

The right answer is that this is a bad question. It's an ambiguous word problem.

14. Jan 22, 2014

You all are all arguing here and where's the OP?In which grade are you studying?Tiven white.

15. Jan 22, 2014

If you are taking a zero as a constant,then the OP will get confused.First we need his educational level,this is not a PhD problem(lol) to talk about all the possibilities.

16. Jan 22, 2014

### Tiven white

Its a question from an undergraduate coarse engineering statics

17. Jan 22, 2014

### tiny-tim

in engineering terms, if something is moving, then it's not stationary

if two surfaces are in relative motion, they don't have the same motion

if you regard everything as moving, then "moving" conveys no information

and "moving" is not a physics or maths term (like "velocity") … in physics or maths, it can usually be omitted from any sentence it's in if it means "having a velocity"

18. Jan 22, 2014

### D H

Staff Emeritus
By the same token, if it's accelerating, then it's not moving at a constant velocity.

I know I've said it before, but once again, this is a lousy question.

19. Jan 22, 2014

### tiny-tim

but …

i] it doesn't say "it's accelerating" (which would be the equivalent of "it's moving"), it says …
ii] "acceleration" is a maths or physics term of art (like "velocity"): it includes deceleration and zero acceleration: and it is quantifiable;
"it is moving" isn't: it means nothing (unless it means it's not at rest!), and one thing can't be more moving than another

EDIT: do engineers talk about "moving parts"?

is the cross-bar of a bike a moving part?

Last edited: Jan 22, 2014