What things in particular do you struggle with?
Here's some key points:
If a question tells you that you can ignore the effects of air resistance then acceleration will either be 9.81ms
-2 or -9.81ms
-2 depending on whether the object is going upwards or downwards.
If we have an object and we throw it upwards it will decelerate so its acceleration will be -g ms
-2. It will come to instantaneous rest when it reaches its max height (so 0 will be your value for v) and then it will accelerate downwards at g ms
-2 .
A falling object will accelerate downwards at g ms
-2 . Its initial velocity (u) will be 0.
The reason for this is that F=ma. If air resistance is ignored then the only force acting on the object is weight. Weight is therefore equal to the resultant force. W=mg so we can equate the two equations: mg=ma. Cancel m from both sides and you have a=g showing that the objects acceleration will be equal to g.
Often you will look at a question and think that you don't have enough of the unknowns to chuck into a SUVAT equation so you have to do a bit of inference here and there. To be honest, this stuff is hard and I struggle with it too so you're not alone here. The more you practice it the more you will begin to see the patterns and begin to know how to approach the questions (so please don't be discouraged). If you have any other questions I would be more than happy to (try to) answer them. I hoped this helped! Have a good day!
