The mechanism shown is used to lift a 80 lb box. THe radius (AB) of the drum is

Question

The mechanism shown is used to lift a 80 lb box. THe radius (AB) of the drum is 2 ft. Length of the arms DE and ABC is 4 ft each. Find the force P required to hold the weight in its current position. Neglect friction and weight of the bars. Hint: Draw the FBD of the drum, the bars ABC and DE and the platform CE. Show equal number of unknowns and equations.

The mechanism shown is used to lift a 80 lb box. The radius (AB) of the drum is 2 ft. Length of the arms DE and ABC is 4 ft each. Find the force P required to hold the weight in its current position. Neglect friction and weight of the bars. Hint: Draw the FBD of the drum, the bars ABC and DE and the platform CE. Show equal number of unknowns and equations.

Explanation / Answer

Using the five equations derived in the attached image, the force can be calculated. The value of theta can be calculated from the fact that the height raised is 4 ft and also the DE = 4 ft, hence the intial DE and current DE form a equilateral triangle. hence theta = 30 degrees.

procedure is in the below link:

http://i.imgur.com/ghN7eK2.jpg?1

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