1. It's decreasing when it travels up, increasing when it goes down
2. a) We live in a world without air resistance, so acceleration is always -9.8m/s^2 or -10. Generally, in physics we say it's -10 because it's an easier number, but go with whatever your teacher tells you to use.
b) There is more than one way to do this question. I am going to find the time it takes to reach the top of its 'flight', and then double it (seeing as it takes the same time to go up and come down)
So a=-10, u=12, v=0, t=?
v=u+at
0=12 - 10t
10t = 12
t=1.2s to reach top => total flight = 2.4s
c) acceleration is constant -> -10m/s^2
d) a=-10, u=12, v=0 (because top of flight), y=? (you can use your 't' value from before, but it is a good idea not to in case you made a mistake)
v^2 = u^2-2ay
144 = 20y
y = 144/20 m = 7.2 I think
e) Flight is symmetrical (from ground level to ground level) -> hits at same speed it leaves at -> 12m/s
f)This depends if the question is with or without air resistance (you never do calculations with air resistance because it is too hard)
Without air resistance, the only force is acceleration downwards, which is constant.
With air resistance, there is also a force in the opposite direction to the direction it's traveling in, which is larger when it is going faster (so at the top there is no air resistance force)