Eva is in a closed dark room. she uses her arm muscles to turn on a lamp. when she moves her hand closer to the lamp, the light heats her hand. the light bounces off the pages of a book and into her eyes. if this room is a closed system, what happens to the total amount of energy in the room? a. it remains constant. b. it increases. c. it decreases. d. it increases, then decreases.

1. How can the room be a closed system if electrical energy is entering?
2. The answer (at least i'm pretty sure) is B it should increase.

Well, we know that the total energy in a closed system remains constant.

The problem with the story of Eva is that she is not in a closed system.  
If the dark room were really a closed system, then she could press the 
button or turn the switch all day, and the lamp could not light.  It needs 
electrical energy coming in from somewhere in order to turn on.

Let's say that Eva used her arm muscles to strike a match and light the 
candle on the table.  Then we would have have food energy, muscle 
energy, chemical energy in the match, chemical energy in the candle, 
heat and light energy coming out of the candle, heat energy soaking into 
her hand, light energy bouncing off of the book and into her eyes ... all 
going on during the story, and the sum total of all of them would remain 
constant. 
sA.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.