Download Energy - Solon City Schools

Energy
General Physics
Kinetic Energy
• Energy a moving object
has
•K = ½
–m: mass (kg)
–V: velocity (m/s)
–K: kinetic energy (joules)
2
mv
Work-Energy Theorem
DK = W or DPE = W
DK = Kf – Ki
DPE = PEf - PEi
Potential Energy
• Stored energy due to gravitational
attraction between Earth and all objects
• PE = mgh
–M: mass (kg)
–g: 9.8 m/s2
–h: height object is from reference
point (meters)
–PE:potential energy (joules)
Conservation of
Energy
• Energy can not be
created nor destroyed, it
can only change forms
Mechanical Energy
• Energy acquired by
objects upon which work
is done
• ME= PE + K
Example Problem
• A 15.0 kg cart is moving with a velocity of
7.50 m/s down a hallway. A constant
force of 10.0 N acts on the cart, and its
velocity becomes 3.20 m/s. What is the
change in kinetic energy of the cart? How
much work was done on the cart?
Example Problem
Ki = ½(15.0 kg)(7.50 m/s)2 = 422 J
Kf = ½(15.0kg)(3.20m/s)2 = 76.8 J
DK =Kf - Ki = 76.8 J – 422 J = -345.2 J
W=DK = - 345.2J
Example Problem
Eesha weighs 505 N. She walks down a
flight of stairs at Solon High School to a
level 5.50 m below her starting point.
What is the change in Eesha’s potential
energy?
Example Problem
PE = (mg)h = (Fg)h = (505N)(-5.50m) =
-2780 J
DPE = PEf - PEi = -2780 J – 0 = -2780 J
Example Problem
• K = 1/2mv2
• Kαm
– Double mass  K doubles
– Cut mass in ½  K is cut in 1/2
• K α v2
– double v  (2v)2 = 4v  K quadruples
– cut v ½  (1/2v)2 = 1/4v  K is cut by 1/4