Unit 1 Review, Extension J Quiz

Pataasin ang iyong marka sa homework at exams ngayon gamit ang Quizwiz!

Examine the energy diagram to the right. For every 1000 J of energy input to a particular television set, on average there are 215 J of energy output through the light interaction, and heat interactions to the surroundings cause their thermal energy to increase 750 J. What is the efficiency of the TV set? Hint: What are the useful energy outputs?

25%

Air conditioners are another device that rely upon heat pumps. Like refrigerator heat pumps, the heat pumps in AC units cool the environment inside a "box" (in this case, a(n) house, apartment, office, etc.) that is separated by a physical barrier (walls, ceilings) from the warmer outside environment. Which of following energy diagrams represents air conditioning in a house that has essentially NO thermal insulation— so that, even with the AC on, it's just as hot inside as outside? (Assume that the AC heat pump is in dynamic equilibrium.)

Diagram C

In the situation illustrated below, (1) Car A is given a push. Almost immediately after the push, Car A collides with Car B, which is stationary. This results in (2) Car A stopping, and Car B moving away from the collision with approximately the same speed Car A had right before the collision. Then Car B gradually slows down, and sometime later, (3) it comes to a stop. Which explanation below best describes the changes in the motion of Car B in terms of energy? (Note: KE=kinetic energy, TE=thermal energy.)

When Car A collides with Car B, there is a contact push/pull interaction between Car A and Car B, during which energy is transferred from Car A to Car B. Car A decreases in KE (to zero), while Car B increases in KE. Because of the increase in KE, Car B speeds up to about Car A's speed just before the collision. After the collision, there is a friction-type contact push/pull interaction between Car B and the floor, during which energy is transferred from Car B to the floor. Car B decreases in KE and both Car B and the floor increase in TE. Because of the decrease in KE, Car B slows down until it stops.


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