1. Physics 1D03 - Lecture 19 Kinetic Energy

2. Physics 1D03 - Lecture 19 Then the Work-Energy Theorem says: The total work done by all external forces acting on a particle is equal to the increase in its kinetic energy. W = ΔK = K f – K i Kinetic Energy Definition Definition: for a particle moving with speed v, the kinetic energy is K = ½ mv 2 (a SCALAR quantity)

3. Physics 1D03 - Lecture 19 Kinetic Energy is measured in joules (1J=1N·m). Kinetic energy is a scalar; the work-energy theorem is a scalar relation. This theorem is equivalent to Newton’s Second Law. In principle, either method can be used for any problem in particle dynamics.

4. Physics 1D03 - Lecture 19 How to deal with friction If there is friction in the system, then: ΔK=W f = -f f d Since ΔK = K f - K i = -f f d Therefore K f = K i - f f d

5. Physics 1D03 - Lecture 19 Example 1 A bartender slides a 1-kg glass 3 m along the bar to a customer. The glass is moving at 4 m/s when the bartender lets go, and at 2 m/s when the customer catches it. Find the work done by friction, and calculate the force of friction.

6. Physics 1D03 - Lecture 19 Example 2 A 6.0 kg block initially at rest is pulled to the right for 3.0m with a force of 12N over a surface. Determine its final velocity if: a) the surface has no friction b) the surface has a coefficient of kinetic friction of 0.15 How else could we solve this problem ???? Try it !!!

7. Physics 1D03 - Lecture 19 Example 3 A block of mass 1.6kg resting on a frictionless surface is attached to a horizontal spring with a spring constant k=1.0x10 3 N/m. The spring is compressed to 2.0cm and released from rest. a) Calculate the speed of the block as it passes the x=0 point. b) Calculate the block’s speed at the x=1.0 cm point. c) Calculate the block’s speed at the x=0cm point if there is a constant frictional force of 4.0 N.