lift (elevator) in a tall building is operated by an electric motor as shown in Figure QB3. The lift car is suspended from a cable that is wrapped around the sheave. The other end of the cable supports a counter-weight. The sheave has a diameter of 550 mm. The counter-weight has a mass of 1750 kg and the combined mass of the lift car and passengers is 2000 kg. The efficiency of the motor is 90%. Air resistance and friction between the cable and the sheave should be ignored. When the lift car is being raised at a constant speed of 2.50 m/s, determine the torque generated by the motor
Plane Trusses
It is defined as, two or more elements like beams or any two or more force members, which when assembled together, behaves like a complete structure or as a single structure. They generally consist of two force member which means any component structure where the force is applied only at two points. The point of contact of joints of truss are known as nodes. They are generally made up of triangular patterns. Nodes are the points where all the external forces and the reactionary forces due to them act and shows whether the force is tensile or compressive. There are various characteristics of trusses and are characterized as Simple truss, planar truss or the Space Frame truss.
Equilibrium Equations
If a body is said to be at rest or moving with a uniform velocity, the body is in equilibrium condition. This means that all the forces are balanced in the body. It can be understood with the help of Newton's first law of motion which states that the resultant force on a system is null, where the system remains to be at rest or moves at uniform motion. It is when the rate of the forward reaction is equal to the rate of the backward reaction.
Force Systems
When a body comes in interaction with other bodies, they exert various forces on each other. Any system is under the influence of some kind of force. For example, laptop kept on table exerts force on the table and table exerts equal force on it, hence the system is in balance or equilibrium. When two or more materials interact then more than one force act at a time, hence it is called as force systems.
A lift (elevator) in a tall building is operated by an electric motor as shown in
Figure QB3. The lift car is suspended from a cable that is wrapped around the
sheave. The other end of the cable supports a counter-weight.
The sheave has a diameter of 550 mm. The counter-weight has a mass of 1750
kg and the combined mass of the lift car and passengers is 2000 kg. The
efficiency of the motor is 90%. Air resistance and friction between the cable and
the sheave should be ignored. When the lift car is being raised at a constant
speed of 2.50 m/s, determine the torque generated by the motor
answer: 750Nm
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