Work and EnergyDefinition of Work

Kinetic EnergyPotential Energy

Conservation of Mechanical EnergyPower

Efficiency

What is work?

The product of Force and distance moved

In the direction of the force

In the direction of the force

Force and displacement must be in the same dimension

Parallel or antiparallelIf parallel, work done is positive

If antiparallel, work done is negativeIf force is perpendicular to

displacement, work done is zero.

Negative work is also referred to asWork done against the antiparallel force

F

sPositive workWork = F x s

Units for Work: Nm or Joule, J

Normal Force

Friction

Tension

Weight

• Work done by• Weight

• Zero• Normal

• Zero• Friction

•Negative

Work = (F cos 30) x s

s

No work forGravity andNormal force

Examples

How do you calculate for total work?

To calculate for total work

Sum of all of the work done by each forceOr

Net force x displacement

Points on Total Work

If net force is zero, total work is also zero.If net work is not zero, then the body is

accelerating.Equation

What is energy?

The stored ability to do work

Kinetic Energy of an object

Stored ability to do work because of its motion.

Work –Energy Theorem

Examples

The work done by gravity

Second case

(Gravitational) Potential Energy of an object

Stored ability to do work as a result of it position.

Conservation of Mechanical Energy

Examples

Power

The rate of doing workWork done per unit time

EquationUnits

Power and Quality of work are not the same.

Efficiency

Power output per power input

ExampleA simple pendulum, consisting of a mass m, is attached to the end of a 1.5 m length of string. If the mass is held out horizontally, which makes a 60°angle with the vertical, and then released from rest, what is its speed at the bottom?

Example

If the 1000- kg roller coaster leaves Point Q from rest, how fast is it traveling at Point R?

Example

If the 1000-kg roller coaster leaves Point Q from rest, what is its speed at Point S?

Past Paper Example

Past Paper Example

Past Paper Example