# Force components question

1. Jan 15, 2008

### david18

1. The problem statement, all variables and given/known data
I need to find the component of W (the 400N force) that is parallel to the slide as in the attached picture. As you can see there is a 24 degree angle between the surface and ground.

2. Relevant equations

3. The attempt at a solution

I should be using simple trigonometry. The equation I am looking for is 400cos66 (or the appropriate version of sin) to give me an answer of 163N. So any help on how to find the triangle that would help me solve this problem would be appreciated.

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2. Jan 15, 2008

### Staff: Mentor

Seems that you already know that the parallel component is $W\cos66$ (which is the same as $W\sin24$). So what do you need a triangle for?

Check this out: Inclined Planes

Last edited: Jan 15, 2008
3. Jan 15, 2008

### blochwave

I think he knows it but doesn't know why

You have that 400 N force going down, break it into the two components, one is the component parallel to the incline, one is the component perpendicular to the incline(going down and to the right, of course)

Do you remember how to add vectors pictorally? Like so
http://liftoff.msfc.nasa.gov/academy/rocket_sci/orbmech/vector_math.gif

for example. Arrange the three vectors so that you have the x component plus the y componet equals the 400 N force going down, and you'll see how you can use trig to solve for the two components magnitudes

EDIT: As you know the answer this trick doesn't help you, but if you ever forget which to use, sin or cos(using the given actual angle, not the complement like you did, ie 24 instead of 66)

If the angle were 0, as in it was just flat, there'd be no component going down the incline(as there would be no incline)it'd all be going straight down, so the correct trig function should equal 0 when the angle is 0, which sin does.

Similarly if you want the component going straight down, it would equal 400 N when the angle was 0, which corresponds with cosine.

Last edited: Jan 15, 2008
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