Hooke’s law states that when a spring is stretched, it pulls back with a force proportional to the amount of the stretch. The constant of proportionality is a characteristic of the spring known as the spring constant. Thus a spring with spring constant k exerts a force f(x2)= kx when it is stretched a distance x.  A certain spring has spring constant k =20 lb/ft. Find the work done when the spring is pulled so that the amount by which it is stretched increases from x =0 to x = 2 ft.

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Hooke’s law states that when a spring is stretched, it pulls back with a force proportional to the amount of the stretch. The constant of proportionality is a characteristic of the spring known as the spring constant. Thus a spring with spring constant k exerts a force f(x2)= kx when it is stretched a distance x. 

A certain spring has spring constant k =20 lb/ft. Find the work done when the spring is pulled so that the amount by which it is stretched increases from x =0 to x = 2 ft.

Expert Solution
Step 1

We need to find the amount of work done in pulling the spring from x=0 to x=2 if the spring with spring constant k exerts a force fx=kx when it is stretched a distance x .

The work done in moving an object from a to b is defined as the limit of this quantity asn.

w=limnm=1n f(xn)x

x=b-anand xm=a+mx

To determine the work done, we first need to evaluate the value of xand xk.

We havex=b-an.

On substituting a=0,b=2, we get

x=2-0n=2n

On substituting a=0 and x=2n in xm, we get

xm=0+m2n=2mn

Step 2

On substituting xm=2mn in fxm we get

fxm=kxm=k×2mn=2kn.m

On substituting the value of fxminw=limnm=1n f(xm)x, we get

w=limnm=1n f(xn)x=limnm=1n2kn.m.2n=limnm=1n4kn2.m=limn4kn2m=1nm

 

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