Warning: Illegal string offset 'html' in /home/hsn/public_html/forum/cache/skin_cache/cacheid_1/skin_topic.php on line 909

Mass on slope formula - HSN forum

Mass on slope formula

3 replies to this topic

#1Steph-x

Newbie

• Members
• 2 posts
• Gender:Female

Posted 27 January 2010 - 04:57 PM

Ok, see in a free body diagram like this (only pretend the F arrow is the pointing the opposite way, I stole it off scholar)? I know the formula is F = W sin20. But I can't figure out why, whenever I try to work it out for myself I get the F and W the other way round.

This is what I'm doing at the minute, where am I going wrong?

sinx = opposite/hypotenuse
sin20 = W/F
W = F sin20.

(PS, if you could explain it by tomorrow it'd be useful. I kind of have my prelim...)

#2Marcus

Site Swot

• Members
• 147 posts
• Location:Aberdeen
• Interests:Guitar - Passed my grade 6 :D :D<br />Write computer programs - won Heriot-Watt programming challenge 2006 and 2007 :D<br />
• Gender:Male

Posted 27 January 2010 - 05:32 PM

the mistake you're making is you are assuming that slope is the triangle you use.

the triangle you have to use the red coloured one, in this diagram,

W is labeled mg, on this, and F would be the bottom most line on this triangle.
=-=-=Marcus=-=-=

#3Steph-x

Newbie

• Members
• 2 posts
• Gender:Female

Posted 27 January 2010 - 05:45 PM

Thank you. I vaguely remember that now...
Why is physics the opposite of common sense?

#4JasMcG

Showing Improvement

• Members
• 10 posts

Posted 09 April 2010 - 03:39 PM

An easy way to remember if it's cos or sin is: perpendiCular = Cos.
That is, there's a "c" in perpendicular and cos.

There is no "s" for sin in parallel, so this wee daft "c" rule is foolproof!

1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users