King Fahd University of Petroleum & Minerals Mechanical Engineering Dynamics ME 201 BY Dr. Meyassar N. Al-Haddad Lecture # 15

Chapter 14 Kinetics of a Particle ; Work & Energy Objectives –To develop the principle of work and energy and app ly it to solve problems that involve force, velocity, and displacement.

Work of a force Force F does work on a particle only when the particle undergoes a displacement in the direction of the force F S U = F. S F U = (F cos  S

The Work of a Force The unit of the work: Joule : 1 joule of work is done when a force of 1 Newton moves 1 meter along its line of action 1 J = 1 N. m English Unit Ib.ft F

Work of a Constant Force Moving Along a Straight Line

Work of a Variable Force

Work of a Weight

Work of a Spring Force Positive work Negative work spring takes work either compressed or Stretched. Therefore, Negative sign is placed

Constant towing force T do positive work, W displacement vector negative work ?? Normal force no displacement no work ! Positive and negative work ?

Example 14.1

14.2 Principle of Work and Energy Useful equation to obtain final speed or displacement

14.3 Principle of Work and Energy for a System of Particles

Work of Friction Caused by Sliding To account for “ internal energy ” which Generate heat; actual displacement should be considered s ’. S’S’

Work and Energy relation Initial K.E + Work Done = Final K.E

Example 14.2 w= 3500 Ib v 1 = 20 ft/s V 2 =0  k =0.5 s= ? x y

Review Example 14-3 Example 14-4 Example 14-6

Example 14-5 m=2kg Smooth v 0 = 1m/s  =  max