program helloworld
integer i
integer, parameter :: out_unit=20
integer, parameter :: in_unit=5

real m
i=1
t=0.0
x=0.0
v=0.0
del=.000005
a=0.0
p0=1.013*10**7
patm=1.013*10**6
vol0=2.0*10**3
area=7.98
m=38.6
topen=.01
open(unit=out_unit,file="results.txt",action="write",status="replace")
open(unit=in_unit,file="data1.txt",action="read")
read(in_unit,*),p0
read(in_unit,*),vol0
read(in_unit,*),m
read(in_unit,*),area
read(in_unit,*),topen
print *, "p0",p0," dynes/cm**2"
print *, "vol0",vol0," cm**3"
print *, "mass",m," gm"
print *, "area",area," cm**2"
print *, "Time to open valve",topen,"sec"
print *, "   Time(sec)        Distance (m)   Velocity (m/sec)    P/P0"
20 if (x.lt.100.0) then
    if (t.lt.topen) then
    p1=(p0-patm)*( 3.0*(t/topen)**2-2.0*(t/topen)**3)
    else
    p1=p0-patm
    endif
    p=(p1)*(vol0/(vol0+area*x))
    a=p*area/m
    v=v+a*del
    x=x+v*del
    i=i+1
    t=t+del
    if (i.eq.101) then
    i=1
    Print *, t,x/100.0,v/100.0,p/p0
    write(out_unit,*) t,x/100.0,v/100.0,p/p0
    endif
   
    if (i.ne.101) then
    goto 20
   
   endif

else
   

30 print *, "1 meter barrel length reached"
print *, "   Time (sec)        Distance (m)   Velocity (m/sec)    P/P0"
print *, t,x/100.0,v/100.,p/p0,i
    endif 
close(out_unit)
close(in_unit)
end program helloworld