# Kinetic Energy

**Topics:**Energy, Kinetic energy, Classical mechanics

**Pages:**2 (385 words)

**Published:**October 15, 2012

Objects have energy because of their motion; this energy is called kinetic energy. Kinetic energy of the objects having mass m and velocity v can be calculated with the formula given below; K=1/2mv²

Kinetic energy is a scalar quantity; it does not have a direction. Unlike velocity, acceleration, force, and momentum, the kinetic energy of an object is completely described by magnitude alone. Like work and potential energy, the standard metric unit of measurement for kinetic energy is the Joule. As might be implied by the above equation, 1 Joule is equivalent to 1 kg(m/s) 2.

Examples

1. Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s. Answer:

KE = 0.5mv2

KE = (0.5)(625 kg)(18.3 m/s)2

KE = 1.05 x105 Joules

2. If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? Answer:

KE = 0.5mv2

KE = 0.5(625 kg)(36.6 m/s)2

KE = 4.19 x 105 Joules

Work-Energy Theorem

Relationship between KE and W: The word done on an object by a net force equals the change in kinetic energy of the object:

Wnet = Kf - Ki

This relationship is called the work energy theorem

W = Fdcosø

When the energy of the body increases, work is positive.

Examples:

1. A boy pushes a 5.00 kg cart in a circle, starting at 0.500 m/s and accelerating to 3.00 m/s. How much work was done on the cart? Answer:

W= Kf- Ki = (0.5)m(vfinal)2 - (0.5)m(vinitial)2

W = (0.5)(5.00)(3.00)2 - (0.5)(5.00)(0.500)2

W = 21.9 J

2. A 1000.0 kg truck accelerates from 20.0 m/s to 25.0 m/s over a distance of 300.0 m. What is the average net force on the truck?

Answer:

W = Kf- Ki = (0.5)m(vfinal)2 - (0.5)m(vinitial)2

W = (0.5)(1000.0kg)(25.0m/s)2 – (0.5)( 1000.0kg)(20.0m/s)2...

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