Help Please!!!

The constant force F of magnitude 3lb is applied to the block. the force has the same direction as the vector u=3i+4j. Find the work done in the direction of motion if the block moves from P1 (3,1) to P2 (9,3). Distance measured in feet.

Question

Help Please!!!

The constant force F of magnitude 3lb is applied to the block. the force has the same direction as the vector u=3i+4j. Find the work done in the direction of motion if the block moves from P1 (3,1) to P2 (9,3). Distance measured in feet.

anonymous · Answer

http://books.google.com/books?id=dtS5M4lx7scC&pg=PA278&source=gbs_toc_r&cad=3#v=onepage&q&f=false pg 314 fig 5.5.27

anonymous · Answer

work = force *  distance

force = 3 lb
distance equals the sqrt( (change in x)^2 + (change in y)^2 )

anonymous · Answer

But i thought work=force * distance * cos of theta

anonymous · Answer

that is true too.

there are just different ways to solve the same thing

so the key in this thing is to find the distance between the two points, can you do it?

anonymous · Answer

yes sqrt (40) right?
$$\sqrt{9-3^{2}+3-1^{2}}$$

anonymous · Answer

the answer in the back says 78/5 ft/lb

anonymous · Answer

(9-3)^2 right? not 9-3^2?

anonymous · Answer

yes thats what i meant

anonymous · Answer

excellent

so 
distance = sqrt(40)
force = 3lb

and
work = force*distance

anonymous · Answer

$$\sqrt{40} \times 3 =18.9736$$

anonymous · Answer

but 78/5 is =15.6