H=
−2g
v
2
−v0
2
=
−20
0−900
=45m
h=v0t- frac{gt ^{2} }{2}h=v0t−
2
gt
2
25=30*t-5t ^{2}25=30∗t−5t
2
5=6*t-t ^{2}5=6∗t−t
2
t ^{2} -6*t+5=0t
2
−6∗t+5=0
D=36-4*5=16D=36−4∗5=16
sqrt{D} =4
D
=4
t1= frac{6+4}{2} =5st1=
2
6+4
=5s
t2= frac{6-4}{2} =1st2=
2
6−4
=1s