32
Chapter 5 Work and Energy Section 1

Chapter 5 Work and Energy

  • Upload
    chase

  • View
    28

  • Download
    0

Embed Size (px)

DESCRIPTION

Chapter 5 Work and Energy. Section 1. Work. The product of the force on an object and the distance through which the object is moved Measured in joules(J) Joule = N x m. Work (cont’d). Equation: W = Force x distance - PowerPoint PPT Presentation

Citation preview

Page 1: Chapter 5 Work and Energy

Chapter 5 Work and Energy

Section 1

Page 2: Chapter 5 Work and Energy

The product of the force on an object and the distance through which the object is moved

Measured in joules(J)

Joule = N x m

Work

Page 3: Chapter 5 Work and Energy

Equation: W = Force x distance

Work is done only when components of a force are parallel to a displacement

If the force is at an angle to the displacement use the equation:

W= FdcosΘ

Work (cont’d)

Page 4: Chapter 5 Work and Energy

A person lifts a 4.5 kg block a vertical distance of 1.2 m. Determine the work done by the person.

Example

Page 5: Chapter 5 Work and Energy

When catching a baseball, a catcher’s glove moves by 10 cm along the line of motion of the ball. If the baseball exerts a force of 475 N on the glove, how much work is done by the ball?

Example

Page 6: Chapter 5 Work and Energy

How much work is done on a vacuum cleaner pulled 3.0 m by a force of 50.0 N at an angle of 30.0° above the horizontal?

Example

Page 7: Chapter 5 Work and Energy

Chapter 5 Work and Energy

Section 2

Page 8: Chapter 5 Work and Energy

The energy of an object that is due to the object’s motion

Measured in joules (J)

Kinetic Energy= ½ x mass x (velocity)²

Kinetic Energy

Page 9: Chapter 5 Work and Energy

Calculate the speed of an 8.0x10⁴ kg airliner with a kinetic energy of 1.1x10⁹ J.

Example

Page 10: Chapter 5 Work and Energy

Two 3.0 g bullets are fired with speeds of 40.0 m/s and 80.0 m/s, respectively. What are their kinetic energies? Which bullet has more kinetic energy?

Example

Page 11: Chapter 5 Work and Energy

The net work done by all the forces acting on an object is equal to the change in the object’s kinetic energy

Equation:◦ Net Work = ΔKE

Work-Kinetic Energy Theorem

Page 12: Chapter 5 Work and Energy

On a frozen pond, a person kicks a 10.0 kg sled, giving it an initial speed of 2.2 m/s. How far does the sled move if the coefficient of kinetic friction between the sled and the ice is 0.10?

Example

Page 13: Chapter 5 Work and Energy

Any object that is at rest has this

SI unit:Joule, J

Potential Energy

Page 14: Chapter 5 Work and Energy

The energy associated with an object due to the object’s position relative to gravity

PEg=mass X acceleration due to gravity X height

Gravitational Potential Energy

Page 15: Chapter 5 Work and Energy

A spoon is raised 21.0 cm above a table. If the spoon and its contents have a mass of 30.0 g, what is the gravitational potential energy associated with the spoon at that height relative to the surface of the table?

Example

Page 16: Chapter 5 Work and Energy

The energy available for use when a deformed elastic object returns to its original configuration

Ep= ½ X spring constant X (distance compressed or

stretched)²

Elastic Potential Energy

Page 17: Chapter 5 Work and Energy

Represented by “k”

Is also called the force constant

Spring Constant

Page 18: Chapter 5 Work and Energy

A spring with a force constant of 5.2 N/m has a relaxed length of 2.45 m. When a mass is attached to the end of the spring and allowed to come to rest, the vertical length of the spring is 3.57 m. Calculate the elastic potential energy stored in the spring.

Example

Page 19: Chapter 5 Work and Energy

The staples inside a stapler are kept in place by a spring with a relaxed length of 0.115 m. If the spring constant is 51.0 N/m, how much elastic potential energy is stored in the spring when its length is 0.150 m?

Example

Page 20: Chapter 5 Work and Energy

There is also chemical potential energy

This deals with the energy found in the food you eat

In one food calorie there are 4.186 J of chemical potential energy

Chemical Energy

Page 21: Chapter 5 Work and Energy

Chapter 5 Work and Energy

Section 3

Page 22: Chapter 5 Work and Energy

The sum of kinetic energy and all forms of potential energy

Mechanical Energy (ME) = Kinetic Energy (KE) + Potential Energy (PE)

ME = KE + ∑PE

Mechanical Energy

Page 23: Chapter 5 Work and Energy

Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.

Conservation of Mechanical Energy MEi= MEf

Conservation of Energy

Page 24: Chapter 5 Work and Energy

MEi = MEf (Equation for conservation of mechanical energy)

ME= KE + PE (Equation for mechanical energy)

KE= ½ mV² (Equation for Kinetic Energy) PE = mgh (Equation for Potential

Energy)

Therefore;½ mVi² + mghi = ½ mVf² + mghf

Conservation of Energy

Page 25: Chapter 5 Work and Energy

Starting from rest, a child zooms down a frictionless slide from an initial height of 3.00 m. What is her speed at the bottom of the slide? Assume she has a mass of 25.0 kg.

Example

Page 26: Chapter 5 Work and Energy

A 755 N diver drops from a board 10.0 m above the water’s surface. Find the diver’s speed 5.00 m above the water’s surface. Then find the diver’s speed just before striking the water.

Example

Page 27: Chapter 5 Work and Energy

Chapter 5 Work and Energy

Section 4

Page 28: Chapter 5 Work and Energy

Measures the rate at which work is done or energy is transformed

Unit: watt, W

P= W Work Δt Time interval

Power

Page 29: Chapter 5 Work and Energy

What is the average power produced by a steam engine that does 6.8 J of work in 3.6 seconds?

Example

Page 30: Chapter 5 Work and Energy

Equation:

P= FV Power = force X speed

Power cont’d

Page 31: Chapter 5 Work and Energy

Given:m= 19 kgV= 2.2 m/s

Solve for power.

Example

Page 32: Chapter 5 Work and Energy

A motor-driven winch pulls a 50.0 kg student 5.00 m up the rope at a constant speed of 1.25 m/s. How much power does the motor use in raising the student? How much work does the motor do on the student?

Example