1. AP Physics Unit 3 Work, Energy & Power
Unit 3 Section 1 Work and Mechanical Advantage
Serway Chapters 7
Glencoe Chapter 10

2. Unit 3 Section 1 Lesson 1 Work and the Work-Energy Theorem Work Objectives
Unit 3 Section 1 Lesson 1 Work Objectives:
Show understanding of the Physics concept of Work
Correctly identify Work from given situations
Recall and show understanding of the formula to calculate Work done
Solve related problems involving Work
Do NOW: If you push a 10.0 Kg object from rest along a frictionless surface with a force of 2.0 N what will the velocity be in 5.00 seconds?
Unit 3 Section 1 Lesson 1 HOMEWORK:
Serway PAGE:207: #’S 3,4,5,7,11,12,13, 15, 17, 20, 22

3. In Class DO THIS in memory of ME
Review Vectors
F = Fi + Fj + Fk i = x j = y k = z
d = di + dj + dk
(F)•(d) = (Fd)x + (Fd)y + (Fd)z
d = √(di2 + dj2 + dk2)
F = √(Fi2 + Fj2 + Fk2)
Review Integrals (Power rule)
(Hooks Spring law)  F = kx
W = ∫if kx dx = ½ k(xfinal2) – ½ k(xinitial2) –
Serway page 188 Examples
Serway PAGE:206 : #’S 1 – 5, 12
Serway PAGE:207: #’S 3, 4, 5, 7, 11, 12, 13, 15, 17, 20, 22

4. Physics concept of WORK
WORK is done only when a constant force applied on an object, causes the object to move in the same direction as the force applied.
NO MOTION  NO WORK

5. Physics concept of WORK
What IS considered as work done in Physics:
You push a heavy shopping trolley for 10 m
You lift your school bags upwards by 1 m
What is NOT considered as work done:
You push against a wall
Jumping continuously on the same spot
Holding a chair and walking around the classroom

6. Physics concept of WORK
WORK can be calculated by:
Work done = Constant x Distance moved {in the direction of motion} force (N) in the direction of force (m)
W = (F)(d)(Cos{Ɵ} )
Units: [J] [N] [m]
SI Unit for Work is JOULE (J)

7. Scalar (“dot”) Product of two Vectors Constant Force and Displacement W = (F)•(d) = (F)(d)(Cos{Ɵ}) F Ɵ d Integral product of two Vectors Non-Constant Force and Displacement W = ∫ Fx dx

8. More Examples of WORK Work done, W = (F)(d)(Cos{Ɵ} ) = (50)(200)(1)
You are helping to push your mother’s heavy shopping cart with a force of 50 N for 200 m. What is amount of work done?
Work done, W = (F)(d)(Cos{Ɵ} )
= (50)(200)(1)
= 10,000 J or
10 kJ (kilo-Joules)

9. More Examples of WORK:
Jack put on his bag-pack of weight 120 N. He then starts running on level ground for 100 m before he started to climb up a ladder up a height of 10 m. How much work was done?
From Physics point of view, no work is done on pack at
level ground. Reason: Lift is perpendicular to movement.
Work is done on pack only when Jack climbs up the ladder.
Work done, W = (F)(d)(Cos{Ɵ} )
= (120)(10)(1)
= J or 1.2 kJ

10. Unit 3 Section 1 Lesson 2 JAN 27 Mechanical Advantage Objectives
Unit 3 Section 1 Lesson 2 MA Objectives:
Show understanding of the Physics concept of Mechanical Advantage
Show understanding of the Physics concept of IDEAL Mechanical Advantage
Correctly identify MA and IMA from given situations
Recall and show understanding of the formula to calculate Efficiency of a System
Do NOW: If you push a 10.0 Kg object from rest along a frictionless surface with a force of 2.0 N what is the work done on the object?
Unit 3 Section 2 Lesson 2 HOMEWORK:
Glencoe PAGE: : #’s 79, 80, 81, 82, 85, 86, (87 – 88)

11. In Class Glencoe Page 268 Challenge Problem Glencoe Page 271 Example 4
Glencoe Page 272 #’s 26 – 28
Unit 3 Section 2 Lesson 2 HOMEWORK:
Glencoe PAGE: : #’s 79, 80, 81, 82, 85, 86, (87 – 88)

12. What is a Simple Machine?
A simple machine has few or no moving parts.
Simple machines make “work” easier

13. Mechanical Advantage Conservation of Energy
Apply the concept of mechanical advantage to everyday situations.
Conservation of Energy
Work in = Work out
F in * d in = F out * d out N
Ideal Mechanical Advantage {IMA}is the RATIO of the
Displacement exerted (in) to the Displacement load (out).
IMA = d in / d out
Mechanical Advantage {MA} is the RATIO of the
Force exerted (in) to the Force load (out).
MA = F out / F in
Efficiency (%) is the RATIO of the (MA) / (IMA) * 100

14. Labs Lab 3-1:1 Lab 3-1:2 Work done on a Flexible Flyer Sled
(inside- a cart)
Lab 3-1:2
Build a simple machine