Work and simple machines

What is work?

• the transfer of energy that occurs when a force is applied over a distance

• the force that draws things to the earth

• the force that generates thermal energy

• the transfer of energy that occurs due to friction

What is power?

• W=Fd

• the rate at which work is done

• How efficient a machine is

• MA=output force/input force

Lifting a stone block 146m to the top of the Great Pyramid required 146,000J of work. How much work was done to lift the block halfway to the top?

• 36.5 N

• 73,000J

• 146,000 W

• 292,000%

Tags

NGSS.MS-PS3-2

Is working being done when HOLDING a suit case

• Yes

• No

• 25J

• 10W

A motor applies a 5000-N force and raises an elevator 10 stories. If each story is 4M tall, how much work does the motor do?

• 75W

• 3.3333%

• 200,000J

• 24 J

Tags

NGSS.MS-PS3-2

NGSS.MS-PS3-4

Calculate the power in wats, needed to mow a lawn in 50 minutes. If the work required is 500,000J.

• 10 W

• 20 W

• 30%

• 30W

What is the equation for efficiency?

• output work / input work x 100

• output force + input force X Work

• Input work/ output work

• MA = output force/input force

What is one IMPORTANT difference about Mechanical Advantage vs Efficiency

• Mechanical Advantage tell how fast a machine works.

• Efficiency is a % while mechanical advantage has no unit.

• Efficiency and Mechanical Advantage are the same thing.

• Efficiency - Mechanical advantage = Watts

How does friction improve efficiency?

• Friction between the moving parts of a machine converts some of the input work into thermal energy

• Friction makes objects easier to move.

• Friction does not affect efficiency.

• Friction decreases the amount of force needed for work to be done.

Tags

NGSS.MS-PS3-3

Which machine efficiency is impossible?

• 1%

• 80%

• 99%

• 100%