Physics for Engineers I
Lecture 6: Work, KE, PE and Conservation law
• Work
• Kinetic Energy; Work-Energy theorem
• Power
• Potential Energy
• Conservative Force
• Conservation of Energy
Review: Work
Seen in week 1: dot product
𝑑𝑙
P
𝐿
Work done over 𝑑𝑙 is 𝐹 ∙ 𝑑𝑙
Total work done is the sum i.e.
Q
𝑄
𝐹 ∙ 𝑑𝑙
𝑃
Anything else?
𝑑𝑙
Q
P
𝐹 ∙ 𝑑𝑙
𝐹 ∙ 𝑑𝑙
𝐹 ∙ 𝑑𝑙
Kinetic Energy and the Work-Energy Theorem
Check consistency: using eqs of motion for uniform
acceleration
Example
Example
Work done
ON the spring
Example
(b)
(b)
Example: Self-study
Power
Example: Self-study
Potential Energy
moving
Example
Elastic Potential Energy
𝑊𝑒𝑙 = −(∆𝑈𝑒𝑙 )
x=0
Spring is neither
stretched nor
compressed
Example
Conservative Force
Conservative Force
Conservation of Energy