CONSERVATION OF MECHANICAL ENERGY What is Mechanical Energy

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CONSERVATION OF MECHANICAL ENERGY What is Mechanical Energy?

CONSERVATION OF MECHANICAL ENERGY What is Mechanical Energy?

Mechanical Energy l. The sum of kinetic energy and all forms of potential energy

Mechanical Energy l. The sum of kinetic energy and all forms of potential energy within a system.

Mechanical Energy l The sum of kinetic energy and all forms of potential energy

Mechanical Energy l The sum of kinetic energy and all forms of potential energy l “ME” l ME = KE + PE

Conservation of Mechanical Energy l Conserved l The means stays constant law is MEi

Conservation of Mechanical Energy l Conserved l The means stays constant law is MEi = MEf or Initial mechanical energy = Final mechanical energy (in the absence of friction)

Conservation of Mechanical Energy l Another way to write the law is MEi =

Conservation of Mechanical Energy l Another way to write the law is MEi = MEf Or 0. 5 mvi 2 + mghi = 0. 5 mvf 2 + mghf

Conservation of Mechanical Energy Example 1 Starting from rest, a child zooms down a

Conservation of Mechanical Energy Example 1 Starting from rest, a child zooms down a frictionless slide with an initial height of 3. 00 m. What is her speed at the bottom of the slide? Assume she has a mass of 25. 0 kg. Here is the formula – you try it first: 0. 5 mvi 2 + mghi = 0. 5 mvf 2 + mghf l

Conservation of Mechanical Energy Example 1 Starting from rest, a child zooms down a

Conservation of Mechanical Energy Example 1 Starting from rest, a child zooms down a frictionless slide with an initial height of 3. 00 m. What is her speed at the bottom of the slide? Assume she has a mass of 25. 0 kg. Here is the formula – you try it first: 0. 5 mvi 2 + mghi = 0. 5 mvf 2 + mghf l 0. 5 (25 kg)(0) + 25 kg(9. 8 m/s 2)(3 m) = 0. 5 (25 kg)vf 2 + 25 kg(9. 8 m/s 2)(0 m) 0 + 735 J = 12. 5 v f 2 + 0 7. 67 m/s = vf

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is held to a slingshot that is stretched 6. 0 cm. The spring constant is 200 N/m. a. What is the elastic PE of the slingshot before it is released?

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is held to a slingshot that is stretched 6. 0 cm. The spring constant is 200 N/m. a. What is the elastic PE of the slingshot before it is released? PEi = 0. 5 kx 2 = 0. 5 (200 N/m)(. 06 m)2 =. 36 J

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is held to a slingshot that is stretched 6. 0 cm. The spring constant is 200 N/m. a. What is the elastic PE of the slingshot before it is released? PEi = 0. 5 kx 2 = ½ (200 N/m)(. 06 m)2 =. 36 J b. What is the KE of the ball just after the slingshot is released?

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is

Conservation of Mechanical Energy l Example 2 A small 10. 0 g ball is held to a slingshot that is stretched 6. 0 cm. The spring constant is 200 N/m. a. What is the elastic PE of the slingshot before it is released? PEi = 0. 5 kx 2 = ½ (200 N/m)(. 06 m)2 =. 36 J b. What is the KE of the ball just after the slingshot is released? KEf = same as PEi =. 36 J, all the initial PE was converted to the final KE

Conservation of Mechanical Energy Example 2 continued c. What is the ball’s speed at

Conservation of Mechanical Energy Example 2 continued c. What is the ball’s speed at the instant it is released? l

Conservation of Mechanical Energy Example 2 continued c. What is the ball’s speed at

Conservation of Mechanical Energy Example 2 continued c. What is the ball’s speed at the instant it is released? KEf = 0. 5 mv 2. 36 J = 0. 5 (10. 0 kg)v 2 8. 5 m/s = v l

Conservation of Mechanical Energy l Video Clip: http: //www. youtube. com/watch? v=JLy. Wac. Uf.

Conservation of Mechanical Energy l Video Clip: http: //www. youtube. com/watch? v=JLy. Wac. Uf. TYY

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