Conservation of Energy

Kinetic and Potential Energy

Kinetic Energy

Energy of motion

KE mv1

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Potential Energy

Energy of Position Gravitational PE—Energy comes from the

Earth’s gravitational attraction on the object and its location

Elastic Potential Energy—comes from the elastic properties of the material such as a spring and its spring constant

Potential Energy

Gravitational Elastic

U mgh U kx1

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Conservation of Mechanical Energy

Mechanical Energy is the sum of the potential and the kinetic energy of an object

The law of conservation of mechanical energy

E KE U 0

Basic Energy Model

There are two kinds of energy, a kinetic energy associated with the motion of a particle oand a potential energy associated with the position of the particle.

Kinetic energy can be transformed into potential energy, and potential energy can be transformed into kinetic energy.

Under some circumstances the mechanical energy is conserved. Its value at the end of a process equals its value at the beginning of the process.

Problem 1

Christine runs forward with her sled at 2.0 m/s. She hops onto the sled at the top of a 5.0 m high, very slippery slope. What is her speed at the bottom?

Problem 2

A 10 g bullet is fired into a 1200 g wood block that hangs from a 150 cm long string. The bullet embeds itself into the block, and the block then swings out to an angle of 40°. What was the speed of the bullet?

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