<p>Does anyone know how to do measurement errors for the subject test? They always occur on the test but I don't know how to face them since most books don't teach them. Here is one question: "A teacher measures and records her own mass to an accuracy of better than half a percent. Which of the following is most likely the mass that she recorded?" Please explain also.</p>
<p>(A) 6.43 k g
(B) 60 k g
(C) 64.3 k g
(D) 600 k g
(E) 643 k g</p>
<p>Any chance that the answer is A?</p>
<p>Well, you should be able to eliminate A, D, E right away. Between B and C, C is more precise (more significant figures).</p>
<p>Answer should be A, </p>
<p>You always report till the error value, in this case (±).005 and the error value is rounded of to nearest value in which we don’t have error => (±).01-.09</p>
<p>The only option correctly adhering to that value is A.</p>
<p>^Uhh, is your teacher a toddler?</p>
<p>I remember doing this somewhere (collegeboard.com?) this question is mean to test your “feel” for the metric system. Just like us in the USA know the average adult is around 150 pounds, someone familiar with the metric system would know that ~60 kg is reasonable for the mass of an adult.</p>
<p>I just did a practice with 36 questions online from collegeboard. It’s at Q20, go check it. The answer is C.
[SAT</a> Physics Subject Test - Physics Questions & Tests](<a href=“The SAT – SAT Suite | College Board”>The SAT – SAT Suite | College Board)
But I don’t really get it. However, the first thing i would do is to eliminate A D and E. Cuz for me they are just non sense lol</p>
<p>please explain why the answer’s C ??</p>
<p>.5% of 64 is .32. therefore she must have recorded the weight as 64.32. But its given that she can record it BETTER than .5% which means that her error will be less than ±.5%.</p>
<p>=> that she can record her accurately as .3 ( as error .32 is = .5% but she can record it better than this)</p>
<p>If you do this for other values, i.e</p>
<ol>
<li>6.43 - error <.03215 (but you can eliminate A as she can’t weight 64.3 N)
2 60 - error < .3 therefore she can measure her mass upto 1 place after decimal which is not shown here. i.e if it would have been 60.0 kg, that would have been correct)</li>
<li>D,E are just absurd as one can’t weight 6000N and 6430N .</li>
</ol>
<p>The answer is C. But how exactly do you do precise measuring? I can’t find a single place to teach me. I recalled on a physics test they had 2 precision question about rulers</p>
<p>It’s more a matter of, do you know what significant figures are. 60 has one significant figure, while 64.3 has three. Slightly more confusing is that 60. and 6.0*10^1 have two significant figures.</p>
<p>The reason why B is incorrect is because reporting a mass of 60 kg leaves a lot of room for error. For example, a mass of 64.9 kg or 55.1 kg can be reported as 60 kg, but the error is around 8%. However, 64.3 kg is more precise and leaves little room for error.</p>
<p>The correct answer is C, 64.3kg . This question is intended to assess your knowledge of realistic values for physical quantities as well as an understanding of experimental error and significant figures. Only 60kg and 64.3kg are likely masses for an adult human. (If you need to compare the choices in pounds to see this, 1kg is approximately 2.2 pounds.) When recording measurements, it is assumed that there is some measurement error in the last digit recorded. For both possible values for the teacher’s weight, 0.5 percent is about 0.3kg. Therefore, a mass recorded to better than this accuracy will indicate tenths of a kilogram.</p>