k=(0.5/90);
a[t_]=k*t;

v[t_]=Integrate[a[t],t]

s[t_]=Integrate[v[t],t]

v2[t_]=Integrate[a[t],{t,0,90}]

s2[t_]=Integrate[v[t],{t,0,90}]

Plot[{10*a[t],v[t],s[t]/10},{t,0,90},PlotStyle->{Blue,Red,Green},AxesLabel->{t,"a[t] v[t] s[t]"},LabelStyle->Directive[Large]]