# Work & Vectors

• May 13th 2008, 05:39 PM
NAPA55
Work & Vectors
Can't figure this one out...

A 35 kg trunk is dragged 10m up a ramp inclined at an angle of 12° to the horizontal by a force of 90N applied at an agle of 20° to the ramp. At the top of the ramp, the trunk is dragged horizontally by the same force for 15 m. Find the total work done.
• May 14th 2008, 05:09 AM
topsquark
Quote:

Originally Posted by NAPA55
Can't figure this one out...

A 35 kg trunk is dragged 10m up a ramp inclined at an angle of 12° to the horizontal by a force of 90N applied at an agle of 20° to the ramp. At the top of the ramp, the trunk is dragged horizontally by the same force for 15 m. Find the total work done.

Split the problem into two parts.

The force up the incline is constant. The displacement up directed up the slope, so
$W = \vec{F} \cdot \vec{s} = Fs~cos(\theta)$
where $\theta$ is the angle the force makes with the displacement.

For the second (flat) part, note that the force is now parallel to the displacment. Apply the same formula. Then add the two answers.

-Dan