Particle Kinetics: Work and Energy Method

Particle Kinetics: Work and Energy MethodJIBZerrudoWork Energy MethodThis is the short cut methodDoes not require vector additionRelatively straight forward and requires only the knowledge of the systems energyOne of the most versatile method in solving dynamics probems

WorkWork

Work done by a constant force:Work done by a varying force:

WorkWork done by a constant force in rectilinear motion

Work and Kinetic EnergyWork and Kinetic Energy is related by the equation

Work done by the gravitational forceWork done by the force of gravity

Work done BY a springWork done BY a spring

General work energy conservation principle

Power and Efficiency

Power The rate of doing work

Power and Efficiency

Efficiency

Work-EnergyA spring is used to stop a 60-kg package which is sliding on a horizontal surface. The spring has a constant k = 20 kN/m and is held by cables so that it is initially compressed 120 mm. Knowing that the package has a velocity of 2.5 m/s in the position shown and that the maximum additional deflection of the spring is 40 mm, determine (a) the coefficient of kinetic between the package and the surface (b) the velocity of the package as it passes again through the position shown.

ApplicationA 10 kg block on top of an inclined plane slides down from rest. What is the speed of the block just before it leaves the incline? The coefficient of kinetic friction between the block and the incline is 0.14 m3 m

Work-Energy

Work-EnergyA block slides from rest down a curved frictionless track and then up an inclined plane as in the figure. The coefficient of kinetic friction between block and incline is 0.2. If the initial height of the block is 10.0 m, what is the maximum height reached by the block? = 30

Work-Energy

Work-Energy

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Example

Prob setPower and Efficiency1. Determine the power input for a motor necessary to lift 300 lb at a constant rate of 5ft/s. The efficiency of the motor is = 0.65.

*2. The engine of the 3500-lb car is generating a constant power of 50 hp while the car is travelling up the slope with a constant speed. If the engine is operating with efficiency of = 0.80, determine the speed of the car. Neglect drag and rolling resistance.

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