1 / 30

Physics

Physics. Session. Work, Power and Energy - 1. Session Objectives. Session Objective. Work done by constant force Work done by variable force Kinetic Energy Work-Energy Theorem Conservative and non-conservative forces Potential Energy and Total Mechanical Energy.

errin
Télécharger la présentation

Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics

  2. Session Work, Power and Energy - 1

  3. Session Objectives

  4. Session Objective • Work done by constant force • Work done by variable force • Kinetic Energy • Work-Energy Theorem • Conservative and non-conservative forces • Potential Energy and Total Mechanical Energy

  5. Work done by constant Force DisplacementS Component of force in the direction of displacement = Fcosq Work done = (Fcosq) S =FS cos

  6. Work by Varying Force Total work done is sum of all terms from xi to xf

  7. Work by Varying Force

  8. Work done on a particle between any two points is independent of the path taken by the particle. Force of gravity & spring Force Frictional Force & Viscous force Work done on a particle between any two points depends on the path taken by the particle. Conservative Forces Non-Conservative Forces

  9. Illustration of principle Conservative Forces : Work done will be same Non-Conservative Force : Work done will be different

  10. Kinetic Energy Energy associated with the motion of a body. Nature : scalar Unit : joules(J)

  11. Work Energy Theorem Work done by Total work done by all the forces acting on a body is equal to the change in its kinetic energy. Conservative forces (Wc) Non-Conservative forces (Wnc) External forces (Wext)

  12. Conservative Forces & Potential Energy Work done by a conservative force equals the decrease in the potential energy. Ui can be assigned any value as only Uis important

  13. Conservative Force: Spring force Force varies with position. Fs=-kx [k :Force constant] Work done in compression/extension of a spring by x = PE stored in the spring

  14. Class Test

  15. Force acting on a body is (a) dependent on the reference frame (b) independent of reference frame (c) dependent on the magnitude of velocity (d) None of these Class Exercise - 1 Solution : A specific force is external in origin and so is independent of reference frame. Hence answer is (d).

  16. A particle moves from a point to another point during which a certain force acts on it. The work done by the force on the particle during displacement is: (a) 20 J (b) 25 J (c) zero (d) 18 J Class Exercise - 2 Solution : Hence answer is (c)

  17. A force F = (a + bx) acts on a particle in the x-direction where a and b are constants. The work done by this force during a displacement from x = 0 to x = d is • zero (b) • (c) 2a + bd (d) (a + 2bd)d Class Exercise - 3 Solution : Force is variable. Hence answer is (b)

  18. A block starts from a point A, goes along a curvilinear path on a rough surface and comes back to the same point A. The work done by friction during the motion is: • positive (b) negative • (c) zero (d) any of these Class Exercise - 4 Solution : Friction always acts opposite to the displacement. Hence answer is (b).

  19. The work done by all forces on a system equals the change in • total energy • (b) kinetic energy • (c) potential energy • (d) None of these Class Exercise - 5 Solution : Statement characterizes kinetic energy. Hence answer is (b).

  20. A small block of mass m is kept on a rough inclined plane of inclination q fixed in an elevator. The elevator goes up with a uniform velocity v and the block does not slide on the wedge. The work done by the force of friction on the block in time t will be • zero (b) mgvtcos2q • (c) mgvtsin2q (d) mgvtsin2q Class Exercise - 6

  21. f vt mg Sin q mg q Solution f = mg sinq as block does not slide. Displacement d = vt Angle between d and f = (90 – q) W = fd cos(90° – q) = mgvt sin2q

  22. A force (where K is a positive constant) acts on a particle moving in the x-y plane. Starting from the origin, the particle is taken along the positive x-axis to the point (a, 0) and then parallel to the y-axis to the point (a, a). The total work done by the force on the particle is: • –2Ka2 (b) 2Ka2 • (c) –Ka2 (d) Ka2 Class Exercise - 7

  23. y 2 a x O 1 a Solution First path: y = 0 Second path: x = a Displacement along x = 0

  24. Under the action of a force, a 2 kg body moves such that its position x as a function of time is given by where x is in metre and t in seconds. The work done by the force in the first two seconds is: (a) 1,600 J (b) 160 J (c) 16 J (d) 1.6 J Class Exercise - 8

  25. Solution Hence answer is (c)

  26. There is a hemispherical bowl of radius R. A block of mass m slides from the rim of the bowl to the bottom. The velocity of the block at the bottom will be: Class Exercise - 9

  27. PE = mgR R 1 KE = mv 2 2 Solution PE = mgR Hence answer is (b)

  28. A block of mass 250 g slides down an incline of inclination 37° with uniform speed. Find the work done against the friction as the block slides down through 1.0 m. (a) 15 J (b) 150 J (c) 1.5 J (d) 1500 J Class Exercise - 10

  29. F=mN N Mg sin37o Mg cos37o 37o mg Solution As the block slides with uniform speed, net force along the incline is zero. Mg sin37° = m N \ Work done by gravity = Work done against friction = Mg sin37° x s = 1.5 J Hence answer is (c)

  30. Thank you

More Related