**Evans SPH 4U1**

**Physics Grade 12**

**Unit 4:
Energy & Momentum**

**Note 1:
Work/Conservation of Energy**

Reference: Chapters 4.1 to 4.4 and 6.3

**You should supplement
these notes with our in-class discussions, proofs and derivations.**

**Work** (scalar,
measured in Joules (N.m):

Energy transferred to an object when a force, acting on the object, moves it through a distance.

The product of the magnitude of the displacement times the component of the force in the direction of the displacement (area under a force displacement graph, dot product of force and displacement).

No work: ~ No work is done on an object if the object doesn't move.

~ No work is done if and are perpendicular (i.e. cos 90 degrees is 0)

~ No work is done if no force is acting to produce the displacement.

**Kinetic Energy:**
(scalar, measured in Joules)

**Work-Energy Theorem:**

Total work done on an object equals the change in the object's kinetic energy, provided there's no change in any other form of energy (i.e. gravitational potential energy). Work = Change in Kinetic Energy

**Example 1:**

A disc slides along a
shuffleboard in 3.0 m. The mass of the disc is 0.5kg. The
coefficient of kinetic friction between the disc and the shuffleboard is 0.4. What is the work done?
**-5.9 Joules**

**Example 2:**

You push a block of mass
2.0 kg across a table by exerting a force of 9.0 N on it. the
magnitude of kinetic friction on the block is 5.0N. The block
starts from rest. What's the speed of the block after it moves
0.3m? **1.1 m/s**

**Homework:**

Page 181 #7

Page 183 # 5,6

Page 186 #5, 7