Because one object can have more things in it. I learned it a t school today.
Answer:
a) 
, b) 
Explanation:
a) The equation for vertical velocity is obtained by deriving the function with respect to time:
The velocities at given instants are, respectivelly:
gravity increases with height. gravity is significantly less on high mountains or tall buildings and increases as we lose height (which is why falling objects speed up) gravity is caused by the Earth spinning. gravity affects things while they are falling but stops when they reach the ground
