Energy By. Jonathan Lee and Harry Chun. What is “energy”? Energy is the ability to do work Potential Energy (PE) is the “possible” ability to do work.

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Presentation transcript:

Energy By. Jonathan Lee and Harry Chun

What is “energy”? Energy is the ability to do work Potential Energy (PE) is the “possible” ability to do work Kinetic Energy (KE) is how much energy a moving object has

Gravitational Potential Energy The potential energy gained or lost as a result of changing it’s vertical position. PE= W= Fd → F= W= mg → d= height → PE= mgh

Elastic Potential Energy The amount of energy stored in a spring when it is compressed or elongated. PE s = (kx²) / 2

Kinetic Energy KE = (mv²) / 2

Practice Question # 1 A 50kg tire is rolling at a speed of 20 m/s. Assuming that there is no friction, what is the kinetic energy of the tire? Solution: KE= (mv²) / 2 KE= ((50kg)(20m/s) ²)/2 KE= (20000kgm²/s²)/2 KE= 10000J

Practice Question #2 Compared to the potential energy of a 25kg box on top of a 50cm shelf, the potential energy of a 50kg box on top of a 25cm shelf is… Solution: Box 1 Box 2 PE= mgh PE= (25kg)(g)(50cm) PE= (50kg)(g)(25cm) PE= J The potential energy is the same

Practice Question #3 A spring, with a spring constant of 10Nm, is elongated to a length of 0.5m. If the spring is elongated 1.0m more, the potential energy of the spring will increase by… Solution: PEs= (kx²) /2 PEs= (k(2x)²) /2 PEs= (4kx²)/2 PEs= 4 * (kx²) /2 Answer: 4 times

Homework Work, power, energy sheet # 138, 145, 149

BONUS QUESTION A 0.5kg bullet is traveling at 20m/s. It then hits a 1kg wooden block that is hanging on a string attached to the ceiling. As a result, the bullet gets embedded in the block, and the wooden block swings upward. Assuming that the string has no mass and there is no friction between the string and the ceiling, what is the maximum height reached by the wooden block?

GOOD LUCK ON MIDYEAR!