Exercise 2: Block System Answer the following questions for the pulley systems s
ID: 1574760 • Letter: E
Question
Exercise 2: Block System Answer the following questions for the pulley systems shown in Fig. 1.2 and 3. 1. How much theoretical Mechanical Advantage is achieved in each case? 2·What will be velocity ratios if weight w is lifted 6 inches and W1 is applied for 40 inches? 3. What is overall efficiency of the system 4. What is the value of wi. w2 and w3, given w=400 lbs? 5. Explain with diagrams a few applications of compound pulleys. . tw w Figure 2: Double Pulley Arrangements Figure 1: Single Pulley Figure 3: Block and tackle Post Lab Exercise: 3 a. What are the reasons for various types of losses in power transmission with regard to pulleys, gears and levers? b. What is meant by 'environmental conditions' w.r.t operations of power transmitting elements?Explanation / Answer
Exercise 2
1. case a.
from force balance
w1cos(theta) + w2 = w
also, w1 = w2
hence
w1(cos(theta) + 1) = w
hence
w/w1 = 1 + cos(theta) > 1 is the advantage
b.
from force balance
w = w3 + w2
but
w1 = w2 = w3
hence
w/w1 = 2
c. from force balance, assuming tension in eache part of the string to be T
3T = w
hence
w/T = 3
2. for x = 6 in
y = 40 in
veloxity ratio Vw/Vw1 = x/y = 0.15
3. overall efficiency is the ratio of the kinetic energy applied by the machine to the total energy provided to the machine
4. W = 400 lbs
case a. w1 = w2 = w3 = 400/(1 + cos(theta))
case b. w1 = w2 = w3 = w/2 = 200 lb
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