Suppose that 2J of work is needed to stretch a spring from its natural length of 30cm to a length of 42cm
how much work is needed to stretch the spring from 35 to 40cm

So Hookies law
Work = kx^(2)

I get

k = 2/144

then I sub k into hookies law to solve for the work

2(5^(2))/144 = 25/72 or approximately 0.35

The answer in the book states that the answer is
25/24 = 1.04J

What am I doing wrong?

Question

Suppose that 2J of work is needed to stretch a spring from its natural length of 30cm to a length of 42cm
how much work is needed to stretch the spring from 35 to 40cm

So Hookies law
Work = kx^(2)

I get

k = 2/144

then I sub k into hookies law to solve for the work

2(5^(2))/144 = 25/72 or approximately 0.35

The answer in the book states that the answer is 
25/24 = 1.04J

What am I doing wrong?

anonymous · Answer

The natural length is 30cm and not 35 cm

anonymous · Answer

oh yeah, sorry I didnt get any sleep last night police raided a neighbors house at 2am in the morning

anonymous · Answer

wow! exciting experience

anonymous · Answer

no more like annoying sirens that interrupted my sleep

anonymous · Answer

only two formulas..nothing complicated at all

anonymous · Answer

thanks yeah i couldnt find the second formula in my text book or notes so yeah

anonymous · Answer

yeah im stilling getting the wrong answer how do I set this up?

anonymous · Answer

and how is the natural length being 30 not 35 significant, it is being stretched by 5cm

anonymous · Answer

see
then in the second part
ur wrk wld be the differnce of the two instances of work: one to stretch it to 40 and one to 35

anonymous · Answer

oh yeah thanks sorry im a mess perfect condition to write a calc 2 midterm today