A 40 kg boy whose leg are 4 cm2 in area and 50 cm long falls through a height of 2 m without breaking his leg bones. If the bones can stand a stress of 1.0 × 108 N/m2, calculate the Young's modulus for the material of the bone.

Loss in gravitational energy = gain in elastic energy in both leg bones.i.e., mgh = 2×(12×stress ×strain ×volume)Here volume     = AL = 4×104×0.5 = 2×10-4 m340×10×2 = 1.0 ×108×strain×2×10-4Strain = 40×101.0×104 = 4×10-2Y = stressstrain = 1.0 × 1084×10-2 = 2.5×109 N/m2