Physics Question

Test Preparation AP Test Preparation
1

<p>I'm stumped. Help!!!</p>

<p>A student is moving a box of books with mass 35 kg up a ramp inclined at 12 degrees with the horizontal. If the box starts from rest at the bottom of the ramp and is pulled at an angle of 25deg with respect to the incline with 185N force, what is the acceleration up the ramp? Assume that coefficient of kinetic friction is 0.27.</p>

<p>So I drew a diagram, and I can't come up with any different answer.
Fn = 257.66
Fk = 69.5689
using the ramp as x,
sum of x components: 26.71
divide that by 35 kg to get .76</p>

<p>But the answer is .90</p>

<p>What did I do wrong?</p>

2

<p>shouldn't the Fn be (cos 12)(35 kg)(9.8)</p>

3

<p>I still don't get the right answer with that. My friend suggested that it could be because I wasn't rounding enough because .76 is remotely close to .9</p>

<p>Still, I think that is too big of an error though.</p>

4

<p>lol i reworked it and got the same answer as you...hmm thats weird</p>

<p>what book is it from? you might want to try <a href="http://www.cramster.com%5B/url%5D"&gt;www.cramster.com&lt;/a> it has the answers worked out (there's a free membership)</p>

5

<p>It's a very basic physics textbook by Serway and Faughn.</p>

<p>Thank you very much for working the problem out, and I'll look into that website.</p>

6

<p>Don't worry, it looks like an error in the problem/answer. Hopefully, this is a practice test, yes? I've noticed several errors in those. If it's the real deal, though, contact the company and ask for a regrading. You are absolutely, 100% correct.</p>

7

<p>Whew! I thought I was going insane because I kept getting that answer. Thank you very much for confirming.</p>

<p>It was actually a random review problem, not for any test or whatever. I'm just learning some basic physics because I'm going into AP Phys C without any previous physics course.</p>

<p>Thanks again!</p>

8

<p>Hey, where are you getting that Fn?</p>

<p>Shouldn't the Fn be equal and opposite to F perpendicular. F perpendicular is -(35 kg) (9.8)(cos 12).</p>

<p>FF= (35kg)(9.8)(cos12)(.27)
FF= 90.59 N</p>

9

<p>wow u guys are good at physics. serway book was hell for me. is it called "College Physics"</p>

10

<p>Oh no, mine is much simpler than College Physics. I have that book too, but I'm not looking at it yet.</p>

11

<p>calculus: there's also the mg(sin theta) component of gravity which is pulling the block down...that had to be added to the friction force i think. anyway you're really good for a beginner. I don't think i even touched inclined planes problems of this level in honors physics (most basic course).</p>

12

<p>Hehe thanks, I guess I have a head start because I'm decent at math. The two subjects are very similar.</p>

13

<p>You'll do well, jenkster. Just out of curiosity, what are you thinking about majoring in?</p>