Warm up problem

Frictionless ramp

Frictionless ramp

Mass: 5 kg.Angle of ramp: 30 degreesLength of ramp: 20 meters

Vf = ?

Energy Energy andand

The Law of Conservation of Energy The Law of Conservation of Energy

Energy

• Energy is the ability to change or cause change.

• If there is no energy, there can be no change.

Most of our energy comes from the sun

• Light from the sun powers all plant growth

• Plants in turn feed all living organisms (either directly or indirectly)

• Plants also become our fossil fuels

Potential and Kinetic Energy• Potential Energy– Energy of what might

happen– Has potential to cause

change– Ex. Compressing a

spring, a ball lifted above the floor (gravity), etc.

Write these 4 scenarios down and predict which shows Potential or Kinetic Energy?1. A bow is drawn back.2. An arrow is shot from the bow.3. A boulder at rest at the top of a hill.4. A boulder rolling at the bottom of a hill.

Which Have Potential or Kinetic Energy?

1. A bow is drawn back. PEPE2. An arrow is shot from the bow. KEKE3. A boulder at rest at the top of a hill. PEPE4. A boulder rolling at the bottom of a hill. KEKE

How Much Energy?

•What is the potential energy of a 2-kilogram potted plant that is on a 2.2 meter-high plant stand?

•What is the kinetic energy of a 3-kilogram ball that is rolling at 2 m/s?

Potential vs Kinetic

• Potential Energy (Ep)– Increases when mass,

gravity or height increases.

– If the height doubles, Ep doubles

Kinetic Energy (Ek)— Increases when mass

increases— If the mass doubles, Ek

doubles— If the velocity

doubles, Ek quadruples (squared)

— What if velocity were tripled?

The Law of Conservation of Energy

• The total energy is the same at all points of an object’s path

Law of Conservation of Energy

• Energy can never be created or destroyed.• Energy can be converted from one form into

another– Kinetic to potential– Potential to kinetic– Kinetic to heat (from friction)

Total Energybefore = Total Energyafter

• A falling rock has a potential energy of 750 J and kinetic energy of 450 J. A few seconds later, it has a potential energy of 400 J. Determine its new kinetic energy.

• A heavy weight that has a mass of 50 kg is lifted using a rope and pulley to a height of 8 meters above a wood post. The rope is cut and the weight falls to hit the post. What is the speed of the weight on impact?

Hint: List the Ep and Ek for each position of the weight.

• A 2,000 kg car moving with a speed of 5 m/sec starts up a hill, and the accelerator and brakes are not working! How high does the car roll before it stops?

• A 0.057 kg car starts from rest at the top of a 0.133-meter hill. Find the speed when it reaches the bottom of the hill.

• A 500 kg roller coaster car starts from rest at the top of a 60-meter hill. Find the speed when it is halfway to the bottom.