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Chapter 7: Q32P (page 318)
A certain motor is capable of doing 3000 J of work in 11 s . What is the power output of this motor?
The power output of this motor is 272.2 W.
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Question: A relaxed spring of lengthstands vertically on the floor; its stiffness is. You release a block of mass from rest, with the bottom of the blockabove the floor and straight above the spring. How long is the spring when the block comes momentarily to rest on the compressed spring?
You lift a heavy box. We’ll consider this process for different choices of system and surroundings.
(a) Choose the box as the system of interest. What objects in the surroundings exert significant forces on this system?
(b) Choose you and the box as the system of interest. What objects in the surroundings exert significant forces on this system?
(c) Choose you, the box, and the Earth as the system of interest. What objects in the surroundings exert significant forces on this system?
You observe someone pulling a block of mass 43kg across a low-friction surface. While they pull a distance of 3m in the direction of motion, the speed of the block changes from 5 m/s to 7 m/s. Calculate the magnitude of the force exerted by the person on the block. What was the change in internal energy (chemical energy plus thermal energy) of the person pulling the block?
During three hours one winter afternoon, when the outside temperature was , a house heated by electricity was kept at with the expenditure of(kilowatt hours) of electric energy. What was the average energy leakage in joules per second through the walls of the house to the environment (the outside air and ground)?
The rate at which energy is transferred between two systems is often proportional to their temperature difference. Assuming this to hold in this case, if the house temperature had been kept at, how manyof electricity would have been consumed?
of water whose temperature isare added to a thin glass containing 800 g of water at(about room temperature). What is the final temperature of the water? What simplifying assumptions did you have to make in order to determine your approximate result?
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