A rope is used to pull a metal box 15 m across the floor in 34 seconds. The rope is held at an angle of 45o with the floor and a force of 628 N is used. How much work does the force on the rope do? How much power is consumed? How efficiently is the force being applied to move the metal box?

Unit 3: Engineering Design

Get out last night’s Homework assignment

Topics Covered

1. Force, Energy, Work, Power, and Efficiency2. Topics in Mechanical Engineering3. Topics in Electrical Engineering4. Engineering Design Process5. Teams and Projects6. PROJECT: Mechanically Controlled Electromagnetic Crane

Unit 3: Engineering Design

1. A rope is used to pull a metal box 10 m across the floor in 30 seconds. The rope is held at an angle of 60o with the floor and a force of 600 N is used. How much work does the force on the rope do? How much power is consumed? How efficiently is the force being applied to move the metal box?

2A. How much work is required to lift a 50 N box to a height of 3 m?

2B. What is the gravitational potential energy of the box once it has been lifted?

2C. If the box is dropped from that height, how fast is it travelling when it hits the ground?

Unit 3 Quiz 1 – 12/01/10Use the Problem Solving Process to Solve and show all work:

1. Machines:1. Devices that use energy to transmit power, force, or motion2. Input and Output

2. Simple Machines:1. Devices that transform the direction or magnitude of a force

without consuming additional energy2. 6 simple machines:

Lever: Lever, Wheel and Axle, PulleyInclined Plane: Inclined Plane, Wedge, Screw

Simple Machines

1. Components:1. Bar/rod2. Fulcrum/pivot 3. Applied Force4. Load

2. Principle of the Lever:1. Static Equilibrium Demonstration

1. SF = 0 – Sum of Forces equals 02. SM = 0 – Sum of Moments equals 0

2. F x dF = L x dL

LEVERS

2nd Class

3rd Class

LEVERS

1. A 1380-kg car is sitting on a hill in neutral. The angle the hill makes with the horizontal is 30o. The distance from flat ground to the car is 200 m. What is the potential energy of the car? How efficient is the force of gravity being applied to the vehicle? What is the work done on the car by gravity? What is the kinetic energy of the car when it reaches the bottom of the hill? What is the velocity of the car when it reaches the bottom of the hill?

2. The manager of a theater knows that 900 tickets were sold for a certain performance. If orchestra tickets sold for $3 each and balcony tickets for $2 each, and if the total receipts were $2300, how may of each kind of ticket were sold?

3. The sum of the digits of a number is 9. If the digits are reversed, the number is increased by 45. What is the original number?

TEST TOMORROWTEST TOMORROWTopics:Topics:

1.1. Types of Communication TechnologyTypes of Communication Technology

2.2. Technical Drawing Types (distinguish between them)Technical Drawing Types (distinguish between them)

3.3. Draw Isometric drawing on Iso graph paperDraw Isometric drawing on Iso graph paper

4.4. Draw missing orthographic linesDraw missing orthographic lines

5.5. Solve 2 word problems (systems of equations)Solve 2 word problems (systems of equations)

UNIT 2: Engineering CommunicationUNIT 2: Engineering Communication

1. Inclined PlaneSlanted surface used to raise an object

2. Wedge1. Double-sided inclined plane2. Used to split, separate, grip3. Wood chisel, firewood axe, doorstop

3. Screw1. Inclined plane wound around a central shaft2. Identified by diameter and threads per inch

INCLINED PLANE

DH

What’s the point???

W = F x d 1. Which path takes less work?

1. Climbing the steep, short cliff face or2. Walking the longer, less steep path

2. It will always take a certain amount of work to lift an object a specific height.

3. The energy required to perform a task will not change.4. We can alter how we do the work or apply the energy.

Mechanical Advantage

1. MA1. Force Multiplier: the number of times a mechanical device

multiplies the applied force.2. Distance Multiplier: “ the distance the applied force travels.3. Let F = 5kg, L = 100kg, and dF = 100cm. What is dL?

1. Is this a force multiplier or a distance multiplier?2. How many times is the applied force multiplied?

4. Equation:1. MA = L / F2. MA = dF / dL

Mechanical Advantage

DH

WHEEL and AXLE1st, 2nd, 3rd Class Lever

WHEEL and AXLE1st, 2nd, 3rd Class Lever

Mechanical Advantage

1. Use dimensional reasoning (and the power-law expression) to determine expressions for the terms on the left side of the equations:

1. W = f(F, d)2. P = f(F, d, t)3. F = f(m, a)4. Eff = f(output, input)

Homework

a) How much work is required to lift a 100-kg box to a height of 1m?

b) Now what is the gravitational potential energy of the load?

c) If the load is dropped from that height, how fast is it travelling when it hits the ground?

d) If a system with a mechanical advantage of 4 is used to lift the load that distance, what is the required applied force?

e) How far must that applied force travel in order to move the load the distance of 5m?

f) If the applied force is in the direction of the displacement, what is the efficiency of the system?

QUIZ – 1 Problem, 6 parts – 2009 SYShow ALL problem solving steps