# Homework Help: Application of Vectors: Work (calc 3)

1. Jul 5, 2005

### ek530n

Hey all,

I'm a bit stuck on a problem on my online homework for my calc 3 class, hopefully someone can help me out.

Suppose that you push with a horizontal force on a box, to push it up a horizontal ramp, as shown in https://instruct2.math.lsa.umich.edu/webwork2_course_files/ma215u05/tmp/gif/2-prob3-pimages/sfig13-3-3.gif [Broken]

If your force is F=22 lbs., the ramp angle a(alpha)=17 degrees above the horizontal and you push the object a distance L=6 feet how much work is done on the box?

Thanks

Last edited by a moderator: May 2, 2017
2. Jul 5, 2005

### dextercioby

What ideas do you have...? I bet the problem is not that difficult.

Daniel.

3. Jul 5, 2005

### ek530n

Well I've tried the plug n' chug method with the numbers give:

W=F(dot)D=|F||D|cos a
W=(22 lbs.)(6 ft.)(cos 17)
W=126.232 ~ 126

But this answer is incorrect, unless the answer registered in the system is incorrect.

4. Jul 5, 2005

### dextercioby

I don't know about your weird American system of units, but the formula is the right one.

Daniel.

5. Jul 5, 2005

### Jameson

I got the same answer. It looks fine to me. Did you put in the correct units?

6. Jul 5, 2005

### Scirel

Force is a vector.

It has X and Y components.

Also remember about Mass x Gravity.

7. Jul 5, 2005

### ek530n

Yes but the formula W=|F||D|cos a can be used instead of W=F(dot)D in order to avoid vectors and instead use magnitudes only.

Also gravity is neglected in this particular problem and units are not required.

8. Jul 5, 2005

### Scirel

Eh? Thats odd. Ive never heard of a problem neglecting gravity before.

also isnt (dot) multiplication.

NOTE: to a helper who is reading this: I really need help with my topci before 2 hours, please!

9. Jul 5, 2005

### ek530n

Is that an attempt to mock me for my choice of words? If you don't have anything relevant to say don't post under this thread.

10. Jul 5, 2005

### Scirel

Wow! Take it easy! I wasnt trying to make fun of you. Geez..

I literally have never seen a problem like that before. How can that be taken as an insult?

anyway, there is one more thing to try.

Are you sure your calculator is in degrees/radians mode? (for whatever the problem calls for)

11. Jul 5, 2005

### lurflurf

You are given the x-component of the force
namely
22 lbs.=(Force)(cos(17 degrees))
You want work
work=force*distance
In other words your cos(17 degrees) should have be sec(17 degrees) or 1/cos(17 degrees).