9.04: Power and Efficiency

Power is defined as

• How much work is done

• The rate at which work is done

• How many things are plugged into an outlet

• The rate at which energy is used

Power does not depend on...

• strength
• work
• time
• any of these

What is the equation for power?

•  $\frac{Work}{Time}$  

•  $\frac{Work}{Energy}$  

•  $mass\times gravity\times height$  

•  $Energy\times Time$  

What is the unit for Power?

• Joules

• Volts

• Watts

• Amps

The unit of power was named after...

• James Watt
• Isaac Newton
• James Joule
• Renee Descartes

A light bulb consumes 100 Watts.  If it is left on for 20 seconds, how much work does it do?

• 5 J
• 2,000 J
• 0.2 J
• 100 J

Tags

NGSS.HS-PS3-1

An engine does 300 J of work in 10 seconds. How much power did it use?

• 3000 N

• 3000 W

• 30 W

• 30 J

If a car weighs 3000 N and drives a distance of 10 m in 2 seconds, how much power does it use?

• 1,500 J

• 60,000 W

• 15,000 W

• 6,000 J

Tags

NGSS.MS-PS3-5

What is the formula for the Percentage Efficiency?

• $\frac{Power\ Out}{Power\ In}\ \times\ 100$

• $\frac{Power\ Out}{Power\ In}\$

• $\frac{Power\ In}{Power\ Out}\$

• $\frac{Power\ In}{Power\ Out}\ \times100\$

How much useful energy is there in this Sankey diagram?

• 90 J

• 10 J

• 100 J

• 80 J