Sparknotes Physics practice test questions

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1

<p>I know Sparknotes is rife with errors (a couple of questions have actually missed necessary graphs entirely....), so I just want to make sure I actually got these questions wrong, since I'm not sure what I did incorrectly:</p>

<p>Which of the following statements about mirrors are true for concave mirrors but not convex mirrors?</p>

<p>I. The focal point is in front of the mirror.
II. The image is real.
III. Incoming rays that hit the vertex are reflected at an equal angle to the axis.</p>

<p>Sparknotes says I and II, but can't concave mirrors produce virtual images when the object is between the focal point and the mirror?</p>

<pre><code> In a certain car, for every 100 J produced in the engine, 80 J is dissipated as heat in the engine, 10 J work the car’s internal electronics, 4 J is dissipated because of air resistance, and 6 J is dissipated because of friction with the road. What is the efficiency of the car’s engine in its capacity to propel the car forward?
</code></pre>

<p>(A) 80%
(B) 14%
(C) 10%
(D) 6%
(E) 4%</p>

<p>I don't know, I consider that the 4 J dissipated due to air resistance helping to propel the car forward as well as the 6 J due to friction, so I said 10%. Sparknotes only considers the 6 J due to friction to count, so they said 6%</p>

<p>Thanks for the help!</p>

2

<p>The first one is definitely a bad question on sparknote’s part. It should be reworded to “the Image can be real” or something similar since you are correct, between the mirror and f the object is virtual.</p>

3

<p>Okay, just making sure, because I tend to only lose points on stupid mistakes. Sometimes my mind goes a little crazy. >_></p>

4

<p>The second question is correct. Friction is the force that is propelling the car forward. (tires and road)</p>

5

<p>Fair enough, I just figured that the car wasn’t gonna go very far if it couldn’t overcome air resistance.</p>

6

<p>@FastNeutrino
the question is just a bit bad. 10J are put into moving the vehicle, but only 6J is the actual propelling force. 4J are wasted by air resistance.</p>

<p>at 250mph, air resistance becomes a big factor.</p>