ASSIGNMENT 1 1. A vertical solid concrete post 32 cm in diameter and 3.0 m long
ID: 1271180 • Letter: A
Question
ASSIGNMENT 1
1. A vertical solid concrete post 32 cm in diameter and 3.0 m long is required to support a load of 9,600 kg. If you ignore the weight of the post, what is
a. the stress in the post?
b. the strain in the post?
c. the change in the post's length when the load is applied?
2. A wire of length L, Young's modulus Y, and cross-sectional area A is stretched elastically by an amount ?L. The restoring force is given by Hooke's Law as k?L. a. show that k = YA L b. show that the work done in stretching the wire must be W = YA (?L)2 2L
3. After landing on an unfamiliar planet, an astronaut constructs a simple pendulum of length 75.0 cm. She finds that the pendulum makes 10 complete swings in 16.4 s. What is the gravitational acceleration on the surface of this planet?
4. A 1.0 kg stone is being whirled at constant speed of 12 m/s in a circle, held on a frictionless horizontal surface by a steel wire which is horizontal. The wire is 4.0 m long and its radius is 1.0 mm. Find the strain in the wire. ??
5. A rod is made of two sections joined end to end. The sections are identical, except that one is steel and the other is brass. While one end is held fixed, the other is pulled to result in a change in length of 1.20 mm. By how much does the length of each section increase?
6. A simple harmonic oscillator has total energy E = 1 kA2 2 where A is the amplitude of oscillation. a. Determine the kinetic and potential energies when the displacement is one half the amplitude. b. For what value of the displacement does the kinetic energy equal the potential energy?
7. The bob of a simple pendulum has a mass of 0.25 kg. The length of the string is 75 cm and its mass is negligible. The pendulum is displaced 15
Explanation / Answer
ques 1
m=9600kg
W=9600*9.8=94.08 kN
dia=32 cm
area A=3.142*(0.32)^2/4=0.08 m^2
a)stress=(W)/A=94.08 kN/0.08 m^2=1176 kN/m2
b)strain=stree/E=1176/ECONCRETE
c) change in length=strain*L=1176*3/ECONCRETE=3528/E