Penalty ice hockey In ice hockeya team is said to be on a power play when at least one opposing player is serving a penalty, and the team has a numerical advantage on the ice whenever both teams have the same number of players on the ice, there is no power play. Up to two players per side may serve in the penalty box, giving a team up to a possible 5-on-3 power play. There are three types of penalties that can result in a power play for the non-offending team: For such penalties, the offending player is ruled off the ice and no substitute for the penalized player is permitted.
As this loss of potential energy occurs, the pendulum bob gains kinetic energy. Yet the total mechanical energy remains approximately 0. We would say that total mechanical energy is conserved as the potential energy is transformed into kinetic energy.
The Example of a Roller Coaster A roller coaster operates on this same principle of energy transformation.
Work is initially done on a roller coaster car to lift to its initial summit. Once lifted to the top of the summit, the roller coaster car has a large quantity of potential energy and virtually no kinetic energy the car is almost at rest.
If it can be assumed that no external forces are doing work upon the car as it travels from the initial summit to the end of the track where finally an external braking system is employedthen the total mechanical energy of the roller coaster car is conserved.
As the car descends hills and loops, its potential energy is transformed into kinetic energy as the car speeds up. As the car climbs up hills and loops, its kinetic energy is transformed into potential energy as the car slows down. Yet in the absence of external forces doing work, the total mechanical energy of the car is conserved.
Conservation of energy on a roller coaster ride means that the total amount of mechanical energy is the same at every location along the track.
The amount of kinetic energy and the amount of potential energy is constantly changing. Yet the sum of the kinetic and potential energies is everywhere the same. This is illustrated in the diagram below. The total mechanical energy of the roller coaster car is a constant value of 40 Joules.
The Example of a Ski Jumper The motion of a ski jumper is also governed by the transformation of energy.
As a ski jumper glides down the hill towards the jump ramp and off the jump ramp towards the ground, potential energy is transformed into kinetic energy. If it can be assumed that no external forces are doing work upon the ski jumper as it travels from the top of the hill to the completion of the jump, then the total mechanical energy of the ski jumper is conserved.
He starts at rest on top of a meter hill, skis down the degree incline and makes a world record setting jump. Assuming that friction and air resistance have a negligible effect upon Lee's motion and assuming that Lee never uses his poles for propulsion, his total mechanical energy would never change.
Of course it should be noted that the original assumption that was made for both the roller coaster car and the ski jumper is that there were no external forces doing work.
In actuality, there are external forces doing work. Both the roller coaster car and the ski jumper experience the force of friction and the force of air resistance during the course of their motion. Friction and air resistance are both external forces and would do work upon the moving object.
In fact, the presence of friction and air resistance would do negative work and cause the total mechanical energy to decrease during the course of the motion.
While the assumption that mechanical energy is conserved is an invalid assumption, it is a useful approximation that assists in the analysis of an otherwise complex motion.The power that a situation can have on a person is simply incredible. This power of situation and obedience go hand in hand, people get caught up in a situation because of the obedience they were taught as children.
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