1. ENGR 215 ~ Dynamics Sections 14.1 – 14.3

2. Conservation of Energy Energy can neither be created nor destroyed during a process, it can only change forms. ` T = Kinetic Energy U = Work

3. Work Sign Convention Work is positive when the force component is in the same direction as the direction of the force.

4. Energy is a State Function We are really concerned about changes in energy from one state to another.

5. The Work of a Force

6. Work along a Path

7. Constant Force along a straight line

8. Work of a Weight

9. Work done by a Spring

10. Sign for Spring Work Spring work is positive if the force on the spring and the displacement are in the same direction. Spring work is negative if the force on the spring and the displacement are in opposite directions.

11. Principle of Work and Energy

12. Lecture Example 1: The 0.5 kg ball of negligible size is fired up the vertical circular track. The plunger keeps the spring compressed 0.08m when s=0. Determine how far the spring must be pulled back and released so that the ball will leave the track at θ = 135˚.

13. Lecture Example 2: A frictionless car with a mass of 1 kg is hooked to a spring (k=10 N/m) on an incline plane with a slope of 1/5. If the car is pulled back 0.5 m from its initial position and released, how fast is the car moving when it passes through the point where the spring is at rest.

14. Lecture Example 3: The 20-kg crate is subjected to a force having a constant direction and a magnitude F=100N. When s=15m, the crate is moving at 8 m/s. Determine the speed when s= 25 m. The coefficient of friction is μ k = 0.25

15. What about this problem on an incline?

16. Lecture Example 4: A 1-kg car attached to a spring was stretched a distance, x, from its rest position, x 0, and released. The velocity of the car was measured at x 0 and plotted below. Determine the spring constant, k, of the spring.