June 30th, 2019, 07:20 AM  #1 
Newbie Joined: May 2019 From: Rostock Posts: 5 Thanks: 0  Typo?
Heya, Looking at an introduction to vectors. In my textbook it gives the example question: "A particle of mass 0.1kg is held at rest on a rough plane inclined at 20° to the horizontal by a friction force, F, acting up the plane. Find the magnitude of F and the normal reaction." The given answer is: "F = 0.1g sin20° = 0.335 N" Is this a typo, or is there something that I'm missing? Thanks very much as ever Theo ps can anyone explain what's happening with the units here? How do you get from grams * degrees to Newtons? 
June 30th, 2019, 07:50 AM  #2 
Newbie Joined: May 2019 From: Rostock Posts: 5 Thanks: 0 
Right. g is gravity, not grams. Gotcha. 
June 30th, 2019, 09:06 AM  #3 
Senior Member Joined: Jun 2019 From: USA Posts: 310 Thanks: 162 
Might I add as an engineering instructor, if any of my students turned in a report with this in it, I would likely take points off and definitely reiterate the importance of clear communication. I would have accepted, "F = (0.1 kg) g sin 20°," or, better yet, "F = mg sinΘ = (0.1 kg)(9.807 m/s²)(sin 20°) = 0.335 N."

June 30th, 2019, 09:21 AM  #4 
Math Team Joined: May 2013 From: The Astral plane Posts: 2,304 Thanks: 961 Math Focus: Wibbly wobbly timeywimey stuff.  

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