A force of 10 lb is required to hold a spring stretched 4 in. beyond its natural length. How much work is done in stretching it from its natural length to 6 in. beyond its natural length?

Question

cj7529 · Answer

Using F=Kx
F = force 
x =extension
you can find the spring constant K of the spring.

Then use the formula again for the 6in extension and find the force required to stretch it to this length.
Then use W=Fx
W=work done
F=force applied
x=distance in direction of the force(or in this case extension of the spring)
One thing though, Lb isn't a unit of force, it's a mass, so you may need to convert that to Newtons

agentjamesbond007 · Answer

Isn't weight a form of force since F=ma?

agentjamesbond007 · Answer

By doing everything, I end up with 15/2, but the answer key says 15/4

cj7529 · Answer

weight is a form of force yeah, but mass isn't.  And Lb is a unit of mass so youd have to use F=ma, like you said.

shamim · Answer

i know work done by a constant force is W=FS
bt now the force is a variable

cj7529 · Answer

And you'd have to work in SI units here, so convert Lb -> Kg and thats probably where that factor of a half is hiding

shamim · Answer

because we need to apply smaller force to extend 1 in.  bt we need to apply higher force to extend this spring 2 in or more

shamim · Answer

i know work done by a force of a spring is $$W=\frac{ 1 }{ 2 }Kx ^{2}$$

shamim · Answer

here K= spring constant
       x= extension of the spring for applying external force

shamim · Answer

anyway F=Kx is ok

shamim · Answer

i think u will get right result by my formula

agentjamesbond007 · Answer

Thank You!

shamim · Answer

u r most welcome