ME 242 Lecture 19 03.13

ME 242 Lecture 19 03.13 - P = dW dt = F • v = T • ω...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 ME 242 Dynamics March 13, 2009 Eric Wang Today’s Key Concepts Chapter 4: Energy of Particles Potential Energy Example Power Efficiency Example Example (prob. 4.2.28) Given: k=22 N/m and m=55 kg Find: length of bungee cord FBD Which forces are conservative? Don’t double-dip with conservative forces kx mg Before and After Work-Energy Equation
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 Substitute the givens Check Could we have solved this with Impulse-Momentum? Could we have solved this with F=ma? Concept Quiz A spring loaded Nerf gun is used to shoot a dart straight up in the air. The dart reaches a maximum height of 24 m. The same dart is shot straight up a second time from the same gun, but this time the spring is compressed only half as far before firing. How far up does the dart go this time (ignore friction and assume an ideal spring)? A) 96 m B) 48 m C) 12 m D) 6 m E) 3 m Power & Efficiency Power is the rate of work Mechanical Efficiency P = dW
Image of page 2
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: P = dW dt = F • v = T • ω power out power in e m = work out work in = Applications Applications 3 Applications Applications For Constant Power If P = constant , can combine with F = ma t 2 − t 1 = 1 P 1 2 mv 2 2 − 1 2 mv 1 2 adx = vdv x 2 − x 1 = 1 P 1 2 mv 2 3 − 1 2 mv 1 3 P = dW dt Example (prob. 4.3.23) • How fast can a 3200 lb car with a 200HP engine accelerate from 0 to 30 mph? (neglect drivetrain losses and air/ road drag) Constant Power Eqn 200 HP = 110,000 ft-lb/s 30 mph = 44 ft/s 3200 lb 99.4 slugs True or False It is possible for power to be negative . 4 Example (prob. 4.3.4) Given: • h = 30 m • e m = 50% • Electricity costs $.15/kW-hr Find: • Cost to pump 1000 liters Efficiency True or False It is possible for efficiency to be negative . Take Home Points • Power • Mechanical Efficiency e m = P = dW dt = F • v power out power in work out work in =...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern