Hey! Sign in to get help with your study questionsNew here? Join for free to post

Hooke's Law questions

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
    • Thread Starter

    Got a couple of simple Hooke's Law questions in a text book I'm using, but I cannot get the answers given in the book.

    Question 1: What force is required to stretch a spring with spring constant 0.2 N/cm a distance of 5 cm?

    Question 2: A vertical spring stretches 5 cm under a load of 100 g. Determine the spring constant.

    The formula for Hooke's Law is F= kx (K = constant and x = extension)

    So for Q1 I simply multiply 0.2 N/cm with 5 cm and get a force of 1 Newton.

    But the book says it's 0.01 N. ??

    For Q2 I work out the force of the 100g mass: (0.1 Kg x 10 N/Kg for gravity = 1 Newton)
    Then I divide Force by Extension which is 1 N / 5 cm = 0.2 N/cm

    But book says it's 0.05 N/cm ??

    What am I doing wrong please?
    • Thread Starter

    Hmmm.... the book clearly states that it is fine to give a constant as N/cm or even N/mm so long as the other unit corresponds. I still don't see how they get those particular answers.

    If question 1 was supposed to be 0.2 N/m then yes... I convert the 5 cm to 0.05 m and then the calculation does result in 0.01 N for the Force. But it is clearly 0.2 N/cm so I leave the 5 cm alone.
Write a reply…


Submit reply


Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: September 20, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Do you like sleeping in a cold room?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.