Mechanical Energy Total Mechanical Energy Total Mechanical Energy

Mechanical Energy Total Mechanical Energy

Total Mechanical Energy (ET): p Energy can be transferred or transformed, never lost Law of Conservation of Energy *If friction negligible n. If friction is not negligible then….

A 56 kg diver runs & dives from the edge of a cliff into the water which is located 4 m below. If she is moving at 8 m/s the instant she leaves the cliff, determine the speed at which she enters the water. Before Jump Eg m = 56 kg g = 9. 8 N/kg h=4 m At Water Level Ek m = 56 kg v = 8 m/s Eg m = 56 kg g = 9. 8 N/kg = h=0 m Ek m = 56 kg v=?

Before Jump At Water Level

A child throws a 0. 2 kg rock at a tree. When the rock leaves the child’s hand, it is moving at 20 m/s & is located 1. 5 m above the ground. How high above the ground does the rock strike the tree if it is moving at 10 m/s at that instant? Throw Eg m = 0. 2 kg g = 9. 8 N/kg h = 1. 5 m Tree Ek m = 0. 2 kg v = 20 m/s Eg m = 0. 2 kg g = 9. 8 N/kg = h= ? Ek m = 0. 2 kg v = 10 m/s

Throw Tree

A 2 kg ball rolls along a frictionless surface. It passes point C at a speed of 20 m/s. What was the speed of the ball at point A? A C 25 m 20 m Point A Eg m = 2 kg g = 9. 8 N/kg h = 20 m Point C Ek m = 2 kg v = ? m/s Eg m = 2 kg g = 9. 8 N/kg = h = 25 m Ek m = 2 kg v = 20 m/s

Point A Point C

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

Work required to set block in motion

You are playing with a toy slider track. The top of the “hump” is 1. 2 m above the level of the slider at the beginning of the track. The average force of friction between the 0. 15 kg slider & the track is 0. 11 N. The distance from point A to point B along the track is 2. 3 m. You propel the slider by applying a constant force of 6. 6 N hoping to get it over the “hump”. How far must you push the slider to ensure that it makes it over the “hump”?

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