Velocity, Acceleration and velocity time graphs

Hi guys,

Im really really struggling with physics and I was wondering if any of you could help me with it or even have good ways of learning it. The subjects I'm struggling with are velocity, acceleration and velocity time graphs. Please help!!!!

Please post any examples you're unsure about.

When it comes to speed-time graphs, it is useful to know that the gradient of the lines on that graph represent acceleration.

Please post any examples you're unsure about.

When it comes to speed-time graphs, it is useful to know that the gradient of the lines on that graph represent acceleration.

Theses are the sorts of questions I mean. Thank you xx

Any particular question you're stuck on?

if I'm quiet honest majority of them :/ but the first once really stumped me xx

Most of these aren't anything to do with speed-time graphs, but what's your approach to the first one??

You need to know that when acceleration is 0, the net force is 0 due to $F=ma$ so the two things are either stationary or going at a constant speed.

If one force is greater than the other, then there is acceleration therefore the objects are increasing in speed and definitely moving.

i would usually think that the tractor is moving because it says the tractor and trailer are accelerating,i so would assume that "A and B are the same" However i have no idea if this is right.

It is not. If there is acceleration, then there is a net force which is not 0. And if the net force is not 0, therefore the two forces do not balance; hence they are not the same.

As I said, take $F=ma$ where $F$ is the net force. We know that $A-B=F$. If it is accelerating then $a\not= 0$ which means that $ma\not= 0$ (because the mass cannot be 0, and neither can the acceleration). Since $F=ma$ we know that $F\not= 0$ therefore $A-B \not= 0$ which means that A and B cannot be equal to one another. If they were, we would get 0 and that is not allowed from our calculations.

One of them must be greater than the other.

In a general sense, you can remember (as said above) that acceleration is the slope of the velocity curve. Also, velocity is the slope of the position curve. Derivatives are just slopes. Therefore, if you're having trouble remembering the formulas for each, learn how to take the derivative of a polynomial equation, and the reverse. (It is calculus, but the technique for this particular kind of function is easily learned.) If you know what acceleration is (because of gravity, or some other thing), you will be able to work that back into a velocity function, and then the position vs time graph.

I remember having a lousy teacher for 11th grade physics and going nuts trying to learn these equations for weeks in fall term, only to be surprised by how easily we powered through them in maybe 15 minutes during spring term in calculus.