Potential and Kinetic Energy

How is all energy divided? Potential Energy Kinetic Energy All Energy Gravitation Potential Energy Elastic Potential Energy Chemical Potential Energy

What is Potential Energy? oEnergy that is stored and waiting to be used later

What is Gravitational Potential Energy? oPotential energy due to an object’s position oP.E. = mass x height x gravity height x gravity Don’t look down, Rover! Good boy!

What is Elastic Potential Energy? oPotential energy due compression or expansion of an elastic object. Notice the ball compressing and expanding

What is Chemical Potential Energy? oPotential energy stored within the chemical bonds of an object

What is Kinetic Energy? oEnergy an object has due to its motion oK.E. =.5(mass x speed 2 )

Conservation of Energy Not created or destroyed as long as the system studied has boundaries, is closed, energy changes to all sorts of different forms, but total energy is constant.

Conservation of Energy Problem Solving Strategies Carefully identify the system. Make sure it is closed Identify the initial and final states of the system. A) If there are no external forces acting on the system, then the total energy of the system is constant: E before =E after B) U g + K = U g + K

Energy practice Large chunk of ice 15.0 kg mass, falls from a roof 8.00 m above the ground. Ignore air resistance Find kinetic energy as it hits the ground. Find its speed just before it hits the ground.

Practice You lift a 2.00kg textbook from the floor to a shelf 2.10 m above the floor. A. What is the book’s gravitational potential energy relative to the floor. B. What is the gravitational potential energy relative to your head, assuming that you’re 1.65 m tall?

More practice A bike and rider approach a hill at a speed of 8.5 m/s. The mass of the bike and rider together is 85kg. A) Find the initial kinetic energy of the system. B) The rider coasts up the hill. If there is no friction at what height will the bike come to a rest?

A 655 N diver leaps into the water from a height of 10.0 m. What is the divers speed just before she hits the water? What is her speed 2.00 m above the water? Conservation of Energy:

White board time Tarzan, mass 85 kg swings down on the end of a 4 m vine from a tree limb 4.0 m above the ground. A) How fast is Tarzan moving when he reaches the ground B) Does your answer to a depend on Tarzan’s mass

Prepared A crane lifts a car 24 m in the air, where it hangs motionless. The car has a mass of 1.3 x 10 3 kg.  How much work does it take to lift the car?  If the car were dropped, how fast would it be moving when it hit the ground?

Prepared Which would take more power a) lifting a fish, mass 11 kg, 12 m in the air in 10 seconds Or b) lifting a monkey (36 kg), 5 meters in the air in 13 seconds.

Prepared A crane applies 25 Watts of power to a Barbie doll for 13 seconds. If the Barbie starts on the ground and the crane lifts straight up, how high is the Barbie doll (mass=30. g) after the 13 seconds.

Prepared A rubber chicken with a mass of 20 g is shot out of a cannon with a velocity of 200 cm/s. If work to accelerate the chicken from rest is done over 1 meter, how much force was applied to the chicken?

In terms of energy, which would you rather do: a) Stop a speeding train, mass 1.3 x 10 4 kg traveling 64 km/hr Or b) Jump from a building (h=50 m) and come to an abrupt stop (Spiderman style). Assume Spiderman’s mass is 70 kg.

Prepared You move a box across a horizontal surface, pulling on a rope that makes an angle of 54 degrees above the horizontal. The tension in the rope is 230 N. How fast is the 6-kg box moving after it was pulled 3 meters?

Prepared A child drops a 1.2 kg ball from the top of a 5.0 m tall building. When the ball has fallen a distance of 2.0 m, what is the velocity of the ball.