Power

SWEET DREAMS, BABY!

ROY LICHTENSTEIN

1966

What is power?

Let’s determine the work, time, and power for you to climb some stairs.

Power

Power

Unit:

J/s = Watt (W)

Example 1

The world record for bench press is 1401 lbs. What information do we need from the video to determine Jimmy Kolb’s Power during the lift? Given our assumptions, what was his power during the lift?

Example 2

A kayaker paddles with a power output of 50.0 watts to maintain a speed of 1.50 m/s.

1. Calculate the resistive force exerted by the water on the kayak.
2. If the kayaker doubles her power output, and the resistive force due to the water remains the same, by what factor does the kayaker’s speed change?

Answers:

1. -33 N
2. Increase by a factor of 2

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Example 3

Human-powered aircraft require a pilot to pedal, as in a bicycle, and produce a sustained power output of about 0.30 hp. The Gossamer Albatross, flown by amateur cyclist and pilot Bryan Allen flew across the English Channel on June 12, 1979 in 2 h 49 min. (1 hp = 746 W; 4186 J = 1 kcal = 1 Cal)

1. How much energy did Allen expend during the flight? (answer: 2.27x10⁶ J)
2. b) How many Snickers candy bars (180 Calories per bar) would the Allen have to consume to be “fueled up” for the flight? (answer: 3 Snickers bars)