1. What is the idea of Work and how does we use this to solve Energy problems
Use “Work” when there is an external force (like friction or pushing/pulling).

2. Work Work = Force x distance
So Work is done when a force is applied for some amount of distance.
If I push on something with 5N of Force for 3 meters than I do 15 Joules of work.
Work can either increase the energy of something or decrease the energy.

3. Work and Energy
So if an object is at rest and I push on it with the force of 5N for 3 meters I will do 15 Joules of work . This 15 Joules of work increases the energy of the object, it increases its energy by 15 Joules.
In this case the Work increased the Kinetic Energy of the object (gave it 15J of Kinetic Energy)

4. Work and Energy Work can also take away energy
A Frictional force usually takes away energy if applied for some distance.

5. Work and Energy
Say an ice skater has a mass of 50kg and is moving at 5 m/s.
KE = ½ (50) 52 = 625 joules
If they slide 3 m across a rough patch of ice where the force of friction is 75N, then the Work done by the friction is 75N x 3m = 225J
To find their final energy….
KEinitial – Work =KE final
625J – 225J = 400J = ½ m vf vf = 4 m/s