physics - d/t graph

[amar21]

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this is from an EK book

they ask which of the following graphs displays a constant velocity... to get to the point, the answer was a Displacement vs Time graph in which the slope was a straight line parallel to the horizontal... (in this case, it would mean the displacement is constant as time is increasing)

I don't get how that is constant velocity? Can someone shed some light on this? I mean, in order for it to be constant, would the displacement not have to move proportionally to the time?

 

[mmc48]

Well, if I understand your question correctly, technically a horizontal line (slope=0) is representative of a constant velocity. That velocity is zero. Zero can technically be a constant velocity.

But, if one of the answer choices showed a straight line, then I would be curious to see their explanation.

Which book are you looking at (page #, etc)? If we can look at the problem ourselves we may be able to help more.

 

[amar21]

physics EK review book, lecture 1 - question 9.

If a Velocity of 0 is considered constant, then it makes sense. Thats what I figured EK was trying to get at... I've just never seen a velocity of 0 called a constant before..


If thats the case, then whats a diagonal line going upwards represent? I mean, a curved line would be acceleration, but whats a straight diagonal line?

 

[mmc48]

Yep, that's what they are looking for. B and D clearly can't be the answer (acceleration not = 0 means it has an acceleration and therefore no constant velocity), and you should be able to knock out A also. So, you're left with C.

Velocity can be considered constant at 0 if you look at it as a vector.

A straight diagonal line also means constant velocity, but in that case the velocity isn't 0. It's either positive or negative depending on the slope.

 

[amar21]

Ah, Ok.

I deduced it had to be C through elimination. But I did not understand or know that a velocity of 0 is still considered constant. Thanks!

 

[Soccerdoc11]

A straight diagonal line also means constant velocity, but in that case the velocity isn't 0. It's either positive or negative depending on the slope.

Wouldn't a straight diagonal line mean constant acceleration so velocity is increasing. (or is this velocity vs. distance graph).

 

[dodjie16]

The slope of a displacement vs. time graph gives you velocity, while the slope of a velocity vs. time graph gives you acceleration.