Section 6.6Mechanical Energy and Its Conservation

Mechanical Energy and Its Conservation How do I solve problems utilizing conservation of mechanical energy?

Conservation If there are no nonconservative forces..

The sum of the changes in kinetic and potential energy is zero

Total Mechanical Energy (E) = KE + PE

Conservation means that E2 = E1 = constant

Conservation - Dropping a rock Total Mechanical Energy

Can calculate this for each stage of the rocks fall

Starts as all potential and changes to all kinetic

Conservation - Dropping a rock

Problem Solving

Set your y = 0

Be consistent with your subscripts

With a spring…

Example In the rock problem… If original height of the rock is 3.0 m, calculate the rocks speed when it has

fallen to 1.0 m above the ground.

Example If the height of the hill is 40 m, and the roller coaster starts from rest,

calculate (a) the speed of the roller coaster at the bottom of the hill, and (b) and at what height the speed will be ½ of (a). Use y = 0 at the bottom of the hill, and assume no friction.

Example Two water slides have the same

length and start at the same height. Both rides start from rest at the same time. (a) Which rider is traveling faster at the bottom? (b) Which rider makes it to the bottom first?

Homework Page 163 # 33 - 41

Power

Units are = Watts

Homework Worksheet