function v = exam5f(t,y,Z,r)
c = 1/sqrt(2);
mu = r/10;
if     t <= 1 - c
   v = -r*y*0.4*(1 - t);
elseif t <= 1
   v = -r*y*(0.4*(1 - t) + 10 - exp(mu)*y);
elseif t <= 2 - c
   v = -r*y*(10 - exp(mu)*y);
else
   v = -r*exp(mu)*y*(Z - y); 
end