A square section beam of fixed length l is designed to deflect a fixed amount δ when loaded in cantilever bending under a fixed force F. Using the formula given below for the mass M of the beam in terms of its density ρ and elastic modulus E, determine which of the following materials would give the lightest beam. Wood: E=12 GPa, ρ=600 kg/m³; Carbon fibre reinforced plastic (CFRP): E=120 GPa, ρ =1600kg/m³, Aluminium: E=75 GPa, ρ=2700 kg/m³; Steel: E =196 GPa, ρ=7800 kg/m³