Time vs Velocity

scoob70

Hi guys - total noob here so apologies .

Can someone explain to me why velocity-time graphs don't start at zero?

Thanks in advance

citrus burst

Are you talking about a graph with velocity on the y axis and time on the x axis?

If this is the case, then you just haven't come across enough. They can start any where they want really. Its just a matter of making sure you are consistent.

Perhaps I don't understand your question fully

scoob70

citrus burst wrote: »

Are you talking about a graph with velocity on the y axis and time on the x axis?

If this is the case, then you just haven't come across enough. They can start any where they want really. Its just a matter of making sure you are consistent.

Perhaps I don't understand your question fully

Hi Citrus - yes that's the one. Did the Accelerating Trolly Method. Then I had to plot the graph then calculate the slope. I was then asked the question - The graph of velocity vs time does not pass through the origin (0,0). Why not?

Thanks for your time.

citrus burst

Well for it to pass through the point (0, 0) it needed to have 0 velocity at time 0. That's what the coordinate (0, 0) means. If, for example the coordinate was (3, 2), this means that at time 3, the velocity was 2. So essentially what this question wants you to realise is that the car(?) was already moving when the clock was started, or the clock started before the car started.

There are a few other things that you may need to take into consideration, like change in direction, but these seem unlikely

Presumably the thing didn't start from rest ?

scoob70

citrus burst wrote: »

Well for it to pass through the point (0, 0) it needed to have 0 velocity at time 0. That's what the coordinate (0, 0) means. If, for example the coordinate was (3, 2), this means that at time 3, the velocity was 2. So essentially what this question wants you to realise is that the car(?) was already moving when the clock was started, or the clock started before the car started.

There are a few other things that you may need to take into consideration, like change in direction, but these seem unlikely

Ahh thanks for that citrus - the other student was operating the cart at the time so I assumed it wasn't moving at the start when I clicked start on the software. But there u go .

scoob70

RoverJames wrote: »

Presumably the thing didn't start from rest ?

Mmm well it was suppose to be from rest - thanks Rover.

scoob70

Think the lights just switched on in my head . So she let go of the cart - the cart was in motion by the time I started recording the speed, therefore the cart was already in motion and obviously wouldn't of started from zero - genius - lol.