Astone is dropped from the roof of a building; 2.00s after that, a second stone is thrown straight down with an initial speed of 25.0m/s, and the two stones land at the same time. how long did it take the first stone to reach the ground? how high is the building? what are the speeds of the two stones just before they hit the ground?

A) -0.5(9.8)*t^2 = -25(t-2) - 0.5(9.8)(t-2)^2 
-4.9t^2 = -25t + 50 - 4.9(t^2-4t+4) 
0 = -25t+50+19.6t - 19.6 
5.4t = 30.4 
t = 5.62962963 s 

b) h = -4.9(5.62962963)^2 
h = -155.2943759 
the building is 155.2943759 m high 

c) speed 0of first stone 
= at 
= 9.8*5.62962963 
= 55.17037037 m/s 
speed of second stone
= v + at
= 25+9.8*3.62962963 
= 60.57037037 m/s

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.