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**Total Mechanical Energy**

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**Total Mechanical Energy (ET):**

Energy can be transferred or transformed, never lost Law of Conservation of Energy *If friction negligible If friction is not negligible then….

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Ex#1 A 56kg diver runs & dives from the edge of a cliff into the water which is located 4m below. If she is moving at 8m/s the instant she leaves the cliff, determine the speed at which she enters the water. Before Jump At Water Level Eg Ek Eg Ek m = 56 kg m = 56 kg m = 56 kg m = 56 kg g = 9.8 N/kg v = 8 m/s g = 9.8 N/kg v = ? h = 4 m h = 0 m =

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Before Jump At Water Level

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Ex#2 A child throws a 0.2kg rock at a tree. When the rock leaves the child’s hand, it is moving at 20m/s & is located 1.5m above the ground. How high above the ground does the rock strike the tree if it is moving at 10m/s at that instant? Throw Tree Eg Ek Eg Ek m = 0.2 kg m = 0.2 kg m = 0.2 kg m = 0.2 kg g = 9.8 N/kg v = 20 m/s g = 9.8 N/kg v = 10 m/s h = 1.5 m h = ? =

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Throw Tree

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Ex#3 A 2 kg ball rolls along a frictionless surface. It passes point C at a speed of 20m/s. What was the speed of the ball at point A? A C 25 m 20 m Point A Point C Eg Ek Eg Ek m = 2 kg m = 2 kg m = 2 kg m = 2 kg g = 9.8 N/kg v = ? m/s g = 9.8 N/kg v = 20m/s h = 20 m h = 25 m =

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Point A Point C

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**So work applied to move mass 5m**

Ex#4 Law of Conservation of Energy A force of 16N is applied to a 400g mass, starting at rest, over a distance of 5m. How long does it take the mass to move 5m? Before After 5m Eg Ek Eg Ek Eg = 0 m = 0.4 kg Eg = 0 m = 0.4 kg v = 0 m/s v = ? Recall, work = energy So work applied to move mass 5m

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**Work required to set block in motion**

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**Ex#5 You are playing with a toy slider track.**

The top of the “hump” is 1.2m above the level of the slider at the beginning of the track. The average force of friction between the 0.15kg slider & the track is 0.11N. The distance from point A to point B along the track is 2.3m. You propel the slider by applying a constant force of 6.6N hoping to get it over the “hump”. How far must you push the slider to ensure that it makes it over the “hump”?

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**Recall, energy= work Recall, work = energy**

Top: Bottom: Recall, energy= work BUT….friction… Recall, work = energy

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