# applied work problem

• Feb 20th 2007, 08:12 PM
ggw
applied work problem
a force F with 8N has direction vector 5i+9j-3k. the force pushes an object on a ramp in a straight line from the point (2,3,0) to the point (4,9,15), where the coordinates are measured in meters. Find the amount of work done by the force
• Feb 21st 2007, 05:17 AM
topsquark
Quote:

Originally Posted by ggw
a force F with 8N has direction vector 5i+9j-3k. the force pushes an object on a ramp in a straight line from the point (2,3,0) to the point (4,9,15), where the coordinates are measured in meters. Find the amount of work done by the force

First the displacement of the object is
(4, 9, 15) - (2, 3, 0) = (2, 6, 15)
which has a magnitude of sqrt(2^2 + 6^2 + 15^2) = 16.278820596

The magnitude of the direction vector of the force is
sqrt(5^2 + 9^2 + 3^2) = 10.723805295
The angle between the force and the displacement is
cos(t) = (5i + 9j - 3k) (dot) (2i + 6j + 15k)/(|5i + 9j - 3k|*|2i + 6j + 15k|)

cos(t) = (10 + 54 - 45)/(10.723805295*16.278820596) = 0.108838299

W = F (dot) s = |F|*|s|*cos(t) = (8 N)*(16.278820596 m)*0.108838299 = 14.174073147 J

Thus W = 14 J.

-Dan