Transcript Power - North Carolina School of Science and Mathematics

Power
The Crab Nebula,
supernova remnant
Power
• Like work, we’ve all heard about power
• But what is it?
• Scientists define power as the amount of
work done divided by the time it takes to
do that work
Power = Work / Time
• Power is work’s rate of change
Definition #2
• As work is related to energy, we can also
define power as the rate of energy use
• Power = Change in Energy/Elapsed Time
Units
• The units of power are Joules/seconds
• 1J/s = 1 Watt (W)
• So if you lift your 1lb weight 10inches in
the air in 1second, your power is 1watt
Power Comparisons
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Light Bulb:
100 W
Vacuum Cleaner:
1,500 W
Dodge Ram w/ Hemi:
250,000 W
Space Shuttle:
11,000,000,000 W
Sun: 400,000,000,000,000,000,000,000,000 W
Question
• A machine does 200J of work over a time
interval of 20s. What is this machine’s
power?
• 10W
How much Energy does a 40W
light bulb consume in 2
minutes?
Machine A performs a certain amount of
work in time t. Machine B performs twice as
much work as 1, but takes 4 times as long.
Machine C performs the same amount of
work as 1, but in ½ the time. Rank the
power of each machine in increasing order.
• 1. A, B, C
2. C, B, A
• 3. C, A, B
4. B, A, C
• 5. B, C, A
Using a 40N force, a pulley system
pulls a box forward at a constant
velocity of 2m/s. What is this pulley
system’s power?