Chapter 9: Q. 14 (page 227)
The motor of a crane uses power P to lift a steel beam. By what factor must the motor鈥檚 power increase to lift the beam twice as high in half the time?
Short Answer
Power becomes 4P , that is four times.
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Chapter 9: Q. 14 (page 227)
The motor of a crane uses power P to lift a steel beam. By what factor must the motor鈥檚 power increase to lift the beam twice as high in half the time?
Power becomes 4P , that is four times.
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A farmer uses a tractor to pull a bale of hay up a incline to the barn at a steady . The coefficient of kinetic friction between the bale and the ramp is . What is the tractor鈥檚 power output?
A kg air compressor is dragged up a rough incline from m to m, where theaxis is vertical. How much work does gravity do on the compressor during this displacement?
When you ride a bicycle at constant speed, nearly all the energy you expend goes into the work you do against the drag force of the air. Model a cyclist as having cross-section area and, because the human body is not aerodynamically shaped, a drag coefficient of .
a. What is the cyclist鈥檚 power output while riding at a steady ?
b. Metabolic power is the rate at which your body 鈥渂urns鈥 fuel to power your activities. For many activities, your body is roughly efficient at converting the chemical energy of food into mechanical energy. What is the cyclist鈥檚 metabolic power while cycling at ?
c. The food calorie is equivalent to How many calories does the cyclist burn if he rides over level ground at?
The left end of a spring is attached to a wall. When Bob pulls on the right end with a 200 N force, he stretches the spring by 20 cm. The same spring is then used for a tug-of-war between Bob and Carlos. Each pulls on his end of the spring with a 200 N force.
How far does the spring stretch? Explain.
Astronomers using a -m-diameter telescope observe a distant supernova鈥攁n exploding star. The telescope鈥檚 detector records of light energy during the first 10 s. It鈥檚 known that this type of supernova has a visible-light power output of for the first 10 s of the explosion. How distant is the supernova? Give your answer in light years, where one light year is the distance light travels in one year. The speed of light is .
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