Change the chapter
The pressure exerted by a phonograph needle on a record is surprisingly large. If the equivalent of 1.00 g is supported by a needle, the tip of which is a circle 0.200 mm in radius, what pressure is exerted on the record in $\textrm{N/m}^2$?
Question by OpenStax is licensed under CC BY 4.0.
$7.80\times 10^{4}\textrm{ Pa}$
Solution Video

OpenStax College Physics for AP® Courses Solution, Chapter 11, Problem 12 (Problems & Exercises) (1:14)

Sign up to view this solution video!


No votes have been submitted yet.

Quiz Mode

Why is this button here? Quiz Mode is a chance to try solving the problem first on your own before viewing the solution. One of the following will probably happen:

  1. You get the answer. Congratulations! It feels good! There might still be more to learn, and you might enjoy comparing your problem solving approach to the best practices demonstrated in the solution video.
  2. You don't get the answer. This is OK! In fact it's awesome, despite the difficult feelings you might have about it. When you don't get the answer, your mind is ready for learning. Think about how much you really want the solution! Your mind will gobble it up when it sees it. Attempting the problem is like trying to assemble the pieces of a puzzle. If you don't get the answer, the gaps in the puzzle are questions that are ready and searching to be filled. This is an active process, where your mind is turned on - learning will happen!
If you wish to show the answer immediately without having to click "Reveal Answer", you may . Quiz Mode is disabled by default, but you can check the Enable Quiz Mode checkbox when editing your profile to re-enable it any time you want. College Physics Answers cares a lot about academic integrity. Quiz Mode is encouragement to use the solutions in a way that is most beneficial for your learning.

Calculator Screenshots

OpenStax College Physics, Chapter 11, Problem 12 (PE) calculator screenshot 1
Video Transcript
This is College Physics Answers with Shaun Dychko. The needle of a record player is being supported by the normal force due to the record and that normal force is going to equal the force of gravity pulling it down and the mass is 1.00 gram which we'll convert into kilograms by multiplying by 1 kilogram for every 1000 grams. The radius of the needle—if we were to look at the end of it—is a circle and it has this radius here of 0.200 millimeters and we'll convert that into 0.200 times 10 to the minus 3 meters because the prefix 'milli-' means times 10 to the minus 3. And this area of the circle is going to be πr squared and we can figure out the pressure then. So the pressure is the force per area so the force is mg and the area is πr squared so we have 1.00 times 10 to the minus 3 kilograms times 9.80 newtons per kilogram divided by π times its radius in meters squared and that is 7.80 times 10 to the 4 pascals.