function y=v(t)
a1=2.5;
a2=-4.5;
v0=0;
vm=60;
if ((t>=0)&(t<vm/a1))
    y=v0+a1*t;
else if ((t>=vm/a1)&(t<(vm/a1-vm/a2)))
        y=vm+a2*(t-vm/a1);
    else
        disp('t is out of range!');
    end
end