Hooke's Law - Question

A spring which obeys Hooke's law has a force constant of 160 N/m

ai) Caculate the extension in mm of the spring produced by a force of 4.0 N

Anyone explain how to do this?

- Thanks.

Reply 1

TimesChanging

f=ke
4/160 = 0.025m
0.025/1000 = 0.000025mm
I think...... Its been a while since physics

Reply 2

Sadbunny11

OP

The answer says 25mm (back of the book)

I thought since we want to find out "extension, 'e'" we would do f/k = e.
I dont get why you did 4/160, since i thought 160 = F and k = 4?

Im probably wrong, but finding it hard to understand :L

Reply 3

hazbaz

11

Original post by TimesChanging

f=ke
4/160 = 0.025m
0.025/1000 = 0.000025mm
I think...... Its been a while since physics

Yep

Reply 4

specialk_698

14

Original post by Sadbunny11

The answer says 25mm (back of the book)

I thought since we want to find out "extension, 'e'" we would do f/k = e.
I dont get why you did 4/160, since i thought 160 = F and k = 4?

Im probably wrong, but finding it hard to understand :L

remember k is (K)Constant force --> so k =160

and f is the force applied --> f = 4

Reply 5

Stonebridge

13

Original post by Sadbunny11

A spring which obeys Hooke's law has a force constant of 160 N/m

ai) Caculate the extension in mm of the spring produced by a force of 4.0 N

Anyone explain how to do this?

- Thanks.

The force constant is a way of saying how strong the spring is.
160 N/m means 160 Newtons needed to stretch it 1 metre.
The fact it obeys Hooke's Law means that if
160N stretches it 1m, then
80N would stretch it 0.5m
40N would stretch it 0.25m etc
For most springs you would only be able to stretch them a small amount.
So if 40N could stretch it 0.25m (250mm)
How much does 4N stretch it?

Mathematically that is written as
F=kx
F is the force need to stretch it a length x and k is the force constant.

Doing it this way is just a case of plugging the numbers in.

(edited 13 years ago)

Reply 6

Sadbunny11

OP

Original post by specialk_698

remember k is (K)Constant force --> so k =160

and f is the force applied --> f = 4

Ah, okay.

Thankyou! :smile:

Reply 7

Stonebridge

13

Original post by TimesChanging

f=ke
4/160 = 0.025m
0.025/1000 = 0.000025mm
I think...... Its been a while since physics

0.025m is 25mm

Reply 8

TimesChanging

Original post by Stonebridge

0.025m is 25mm

How embarrassing. No really it is. Im doing A-level physics.

Reply 9

Stonebridge

13

Original post by TimesChanging

How embarrassing. No really it is. Im doing A-level physics.

I wouldn't worry too much. :smile:

I've done the same myself in the past. (Divided instead of multiplied) Usually the result of being in too much of a hurry to complete a reply and not concentrating on what I'm doing.