1. Adv Physics
Chapter 5
Sections 3 & 4

2. Work-Energy Theorem
When a net force does work on an object, the total work done is equal to the object’s change in KE or
When an object’s KE changes, the change in KE of the object is equal to the total work done by the object
ΔKE = ΣW

3. Sample Problem
A girl pulls a wagon along a level path for a distance of 45 m. The handle of the wagon makes an angle of 20 degrees with the horizontal and she exerts a force of 85 N on the handle. If the wagon starts from rest, find the work done and the change in kinetic energy of the wagon.
3594.3J J

4. Sample Problem
A 50,000 kg space probe is traveling at a speed of 11,000 m/s through deep space. No forces act on the probe except that generated by its own engine. The engine exerts a constant force of 400,000 N directed parallel to the displacement. The engine fires continually while the probe moves in a straight line for a distance of 2,500,000 m. Determine the final speed of the probe.
m/s

5. Sample Problems
A 58 kg skier is coasting down a 25 degree slope. A kinetic frictional force of 70 N opposes her motion. Near the top of the slope, the skier’s speed is 3.6 m/s. Ignoring air resistance, determine the speed at a point that is 57 m downhill.
18.6 m/s

6. Gravitational Potential Energy
Energy an object has due to its elevated position
Ug= GPE = mgh
where Ug = GPE = gravitational PE
m = mass
g = acceleration due to gravity
h = height (relative to a reference point)
[Ug] = J

7. Sample Problems
A 50 kg mass of steel is raised 5 m. What is its gravitational potential energy?
A 65 kg diver is poised at the edge of a 10 m platform. Calculate the diver’s gravitational potential energy relative to the water.
2450 J
6370 J