1. Phy100: More on Energy conservation Mechanical energy (review); Goals: Work done by external forces; Understand conservation law for isolated systems.

2. A pebble tossed into the air

3. Q1 The pebble is tossed up with speed 10m/s. Which of the following is correct ? A)It reaches a maximal height of about 10m when all kinetic energy is converted into the potential energy. B) It reaches a maximal height of about 10m when the speed is maximal. C) It reaches a maximal height of about 5m when the speed is maximal. D) It reaches a maximal height of about 5m when the speed is zero.

4. Q2 Your result (i.e. the location of the turning point or the maximal height above the ground) depends on A) Mass and initial velocity; B) Choice of the zero point for the potential energy; C) Mass and gravitational acceleration; D) Initial velocity.

5. Simulations of energy conservation--- Energy skate park

6. Work and Energy Work done by an external force over a distance d is W= + F d if the force is along the direction of motion; W= -Fd if the force is opposite to the direction of motion. Power = W/ T, work done per unit time.

7. Energy transfer, work and energy conservation for mechanical systems W= +Fd or -Fd

8. Q3 A block of mass 1kg with zero initial velocity is pushed on a frictionless surface over a distance 1m; the exerted force is 2N. The final velocity is A) 1m/s; B) 4m/s; C) 2m/s; D) None of above.

9. Q4 A block of 2kg slides on a surface with an initial velocity 5m/s. The frictional force between the block and the surface is 5N. How long can the block travel before coming to a stop? A) 1m; B) 10m; C) 5m; D) 4m..