1. Consider gravitational force:
8 Potential Energy
Gravitational Potential Energy:
U=mgh SI unit: J
Consider gravitational force: hi hf W h
Wg =ΔK= - ΔU; E=Kf+Uf=Ki+Ui

2. Conservative force: work done by these force to move an object between any two points is independent of the path taken. woke done by conservative forces, Mechanical Energy is conservative. K+U=constant

3. Slide m=80 kg, vi=0 Find the speed the person at the bottom of slide?

4. Calculating a home run
A player hits a 0.15-kg baseball over the outfield fence. The ball leaves the bat with a speed of 36 m/s, and a fan in the bleachers catches it 7.2m above the point where it was hit. Assuming frictional force can be ignored, find (a) the kinetic energy of the ball when it is caught and (b) its speed when caught.

5. Skateboard exit ramp
A 50-kg skateboard enters a ramp moving horizontally with a speed of 8.0 m/s and leaves the ramp vertically height with 1.4 m. Find final velocity vf, assuming no energy loss to frictional forces

6. Potential energy of a spring, the displacement x, U=1/2kx2 Energy of spring E=K+U=1/2mv2+1/2kx2 Problem: K=4000 N/m, m=60kg, How the height?
0.5m

7. Ex. M=1.7kg, k=955N/m, x=4.6cm Find vi

8. Conservative forces, such as gravity and spring force.
Work done by Non conservative forces, such as friction, air resistance.
Work-energy
Wtotal=ΔK
Wgravity+Wspring+Wnc=ΔK
Wgravity+Wspring= - ΔU
Wnc=ΔU+ΔK=ΔE

9. Ex. Falling leaf Find air resistance force on leaf?
Vi=0
Vf=1.3 m/s
5.3 m