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+//Exa 4.2
+clc;
+clear;
+close;
+//given data
+k=40;// in W/mK
+rho=7800;// in kg/m^3
+C=450;// in J/kgK
+d=20*10^-3;// in m
+r=d/2;
+t_i=400;// in degree C
+t=85;// in degree C
+t_infinite=25;// in degree C
+h=80;// in W/m^2K
+//l_s=V/A = (4/3*%pi*r^3)/(4*%pi*r^2) = r/3
+l_s=r/3;// in m
+Bi= h*l_s/k;
+// since Biot number is less than 0.1, hence lumped heat capacity system analysis can be applied
+
+// Part(a)
+// Formula (t-t_infinite)/(t_i-t_infinite)= %e^(-h*A*toh/(rho*V*C)) = %e^(-h*toh/(rho*l_s*C))
+toh= -log((t-t_infinite)/(t_i-t_infinite))*(rho*l_s*C)/h;// in sec
+disp(toh,"The time require to cool the sphere in sec");
+
+// Part(b)
+// dtBYdtoh = h*A*(t_i-t_infinite)/(rho*V*C) = h*(t_i-t_infinite)/(rho*l_s*C)
+dtBYdtoh = h*(t_i-t_infinite)/(rho*l_s*C);// in degree C/sec
+disp(dtBYdtoh,"Initial rate of cooling in degree C/sec");
+
+// Part(c)
+A=4*%pi*r^2;
+toh=60;
+q_in= h*A*(t_i-t_infinite)*%e^(-h*toh/(rho*l_s*C));// in watt
+disp(q_in,"Instantaneous heat transfer rate in watt");
+
+// Part(d) Total energy transferred during first one minute
+V=4/3*%pi*r^3;
+TotalEnergy = rho*C*V*(t_i-t_infinite)*(1-%e^(-h*toh/(rho*C*l_s)));
+disp(TotalEnergy,"Total energy transferred during first one minute in watt")
+
+// Note: Answer of first and last part in the book is wrong