2 Nm of work is required to stretch a spring from its natural length 30 cm to 42 cm.

How much work is needed to stretch the spring from 35 cm to 40 cm?

Question

2 Nm of work is required to stretch a spring from its natural length 30 cm to 42 cm.

How much work is needed to stretch the spring from 35 cm to 40 cm?

anonymous · Answer

1st : this is a physics problem. Next: k=-f/x or k=2/12=1/6.
I'm not sure about the actual answer. I'm trying to decide if it is orthodox to take the work required to stretch to 40 cm, then to subtract the work required to stretch to 35 cm.

anonymous · Answer

That actually just gets me -5/6, which doesn't make sense.

anonymous · Answer

This is an application problem of integrals. The force used to stretch a spring is from hookes law; what I did:

find the force to stretch 30 to 42
from this force find the k (spring constant)
with k known, find force to stretch 35  to 40
with this force, find the work

but my answer didnt match with the books!

anonymous · Answer

Try $$W= \int\limits_{35}^{40} -1/6 x dx$$

anonymous · Answer

which is -125/4