General Physics I Fall 2017 Show all work for full credit. PHYS 241-002 Exam 3 (
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Question
General Physics I Fall 2017 Show all work for full credit. PHYS 241-002 Exam 3 (Print) Numbers without correct units will not get you any point. Correct numbers with incorrect significant figures will only get you 80% of the points. 1. Describe the Work-Energy theorem. (7) Under what circumstances the mechanical energy will be conserved? What happens when mechanical energy is not conserved? (8) 2. A robot travels on a frictionless surface in a one- dimensional motion. The force acting on the robot is programmed to be as shown to the right as a function of position. The motion consists of three different periods, 0 _ 4 m, 4 m _ 8 m and 8 m-12m. (a) Identify the period that has the greatest work done on the cart, and determine the value of the work. (10) 25 20 2 15 10 2 8 12 Distance from Origin (m) b) What is the total work done on the cart during the entire 12 m of travel (10Explanation / Answer
1)
Work-energy Theorem
Work-energy theorem states that the work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. This definition can be extended to rigid bodies by defining the work of the torque and rotational kinetic energy.
Mechanical energy conservation
The principle of the conservation of mechanical energy states that the total mechanical energy in a system (i.e., the sum of the potential plus kinetic energies) remains constant as long as the only forces acting are conservative forces.
So, the mechanical energy of a system is conserved under the circumstance that the only forces acting are conservative forces.
When non-conservative forces(friction, etc) are present in the system, the mechanical energy is not conserved. A non-conservative force increases/decreases the mechanical energy. When the mechanical energy is not conserved, then energy transformation takes place. Mechanical energy is converted to other form (like hea, etc) or the reverse, i.e. other form of energy changing to mechanical energy takes place.
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