Work done on block by spring and friction

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
1 reply · 18K views
JennV
Messages
21
Reaction score
0

Homework Statement



In the system shown in the figure, suppose the block has a mass of 2.7 kg, the spring has a force constant of 480 N/m, and the coefficient of kinetic friction between the block and the floor is 0.18.

Find the work done on the block by the spring and by friction as the block is moved from point A to point B along path 2.

Diagram:
http://img706.imageshack.us/img706/5935/walker4ech08pr006.jpg

Homework Equations



Wspring = 1/2kx^2
Wfriction = -uk*m*g*x

The Attempt at a Solution



Wspring = 1/2(480)(0.020)^2 = 0.096
Wfriction = -(0.18)(2.7)(9.81)(0.020) = -0.0953532

I inserted these values into the system, but it said that my sign for Wspring is wrong, so I switched it to a negative. It stopped saying anything about my signs, but it won't say that it is correct. I'm not sure what is wrong...
THANKS.
 
Last edited by a moderator:
Physics news on Phys.org
Although the work done by the spring only depends on the initial and final positions, the work done by friction depends on the entire path taken---i.e. what's the distance during which friction does work?