Question

A 150-mm-long vertical rod is rigidly secured at its upper end and a collar is provided at the lower end. A weight of 15N is allowed to fall freely on the collar through a distance of 15mm. What is the maximum stress developed in the upper part if the length of the upper part is 90mm. The diameters of the upper and lower parts are 16 and 8mm, respectively. The bar is made of copper (Fig. 1.56). E =108 kN/mm². (Neglect loss of PE due to extension in bar).

Answer 1

W = 15 N 

h = 15 mm 

Wh = 15 × 15 = 225Nmm

Say stress developed in the upper part is σ₁ and stress developed in the lower part is σ₂