Dynamics_Hibbeler_CH18_5

# Dynamics_Hibbeler_CH18_5 - PLANAR KINETICS OF A RIGID BODY:...

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PLANAR KINETICS OF A RIGID BODY: CONSERVATION OF ENERGY In-Class Activities : Check Homework Reading Quiz Applications Potential Energy Conservation of Energy Concept Quiz Group Problem Solving Attention Quiz Today’s Objectives: Students will be able to: a) Determine the potential energy of conservative forces. b) Apply the principle of conservation of energy.

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READING QUIZ 1. Elastic potential energy is defined as ___________. A) + (1/2) k (s) 2 B) - (1/2) k (s) 2 C) + (1/2) k (v) 2 D) None of the above 2. The kinetic energy of a rigid body consists of the kinetic energy due to ___________. A) translational motion and rotational motion B) only rotational motion C) only translational motion D) the deformation of the body
APPLICATIONS The torsion springs located at the top of the garage door wind up as the door is lowered. When the door is raised, the potential energy stored in the spring is transferred into the gravitational potential energy of the door’s weight, thereby making it easy to open. Are parameters such as the torsional spring stiffness and initial rotation angle of the spring important when you install a new door?

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APPLICATIONS (continued) Are the gravitational potential energy of the hood and the torsional spring stiffness related to each other? If so, how? Two torsional springs are used to assist in opening and closing the hood of the truck. Assuming the springs are uncoiled when the hood is opened, can we determine the stiffness of each spring so that the hood can easily be lifted, i.e., practically no external force applied to it, when a person is opening it?
CONSERVATION OF ENERGY (Section 18.5) The conservation of energy theorem is a “simpler” energy method (recall that the principle of work and energy is also an energy method) for solving problems. Once again, the problem parameter of distance is a key indicator for when conservation of energy is a good method to solve a problem. If it is appropriate for the problem, conservation of energy is easier to use than the principle of work and energy. This is because the calculation of the work of a conservative force is simpler. But, what makes a force conservative?

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CONSERVATIVE FORCES A force F is conservative if the work done by the force is independent of the path . In this case, the work depends only on the
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## Dynamics_Hibbeler_CH18_5 - PLANAR KINETICS OF A RIGID BODY:...

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