Hey there Sign in to join this conversationNew here? Join for free

Resolving forces - OCR M1 Questions

Announcements Posted on
    • Thread Starter
    • 4 followers
    Offline

    ReputationRep:
    Hi guys,

    I'm struggling to see where I'm going wrong with these questions, if any one could help I'd be thankful:

    1) A shopper pushes a supermarket trolley in a straight line towards her car with a force of magnitude of 20N, directed downwards at an angle of 15 degrees to the horizontal. Given that the acceleration of the trolley is 2.4ms^2, calculate its mass. Also find the magnitude of the normal contact force exerted on the trolley by the ground.

    - I found the mass to be 8.05kg (3 s.f) which is correct however when it came to finding the normal contact force I was confused. I did R+20sin15 = 8.05(9.8), which led me to the wrong answer - can anybody explain why?


    2) A child's toy of mass 5kg is pulled along level ground by a string inclined at 30 degrees to the horizontal. Denoting tension in the string by TN find, in terms of T, an expression for the normal contact force and deduce that T cannot exceed 98.

    I got this right, but think it was more down to guess work than anything else -if somebody could post their method for it, it would really help.

    Thanks in advance.
    • 29 followers
    Offline

    (Original post by Choppyy)
    Hi guys,

    I'm struggling to see where I'm going wrong with these questions, if any one could help I'd be thankful:

    1) A shopper pushes a supermarket trolley in a straight line towards her car with a force of magnitude of 20N, directed downwards at an angle of 15 degrees to the horizontal. Given that the acceleration of the trolley is 2.4ms^2, calculate its mass. Also find the magnitude of the normal contact force exerted on the trolley by the ground.

    - I found the mass to be 8.05kg (3 s.f) which is correct however when it came to finding the normal contact force I was confused. I did R+20sin15 = 8.05(9.8), which led me to the wrong answer - can anybody explain why?
    I don't know what your reasoning is for arriving at that equation, however:

    Sum of vertical forces is zero, since the trolley isn't going into the ground or flying up into the air.

    So magnitude of downwards forces = magnitude of upward forces.

    Viz. mg + 20 sin15 = R
    • Thread Starter
    • 4 followers
    Offline

    ReputationRep:
    (Original post by ghostwalker)
    I don't know what your reasoning is for arriving at that equation, however:

    Sum of vertical forces is zero, since the trolley isn't going into the ground or flying up into the air.

    So magnitude of downwards forces = magnitude of upward forces.

    Viz. mg + 20 sin15 = R
    I did it as I didn't realise the force was acting downwards - cheers, don't need any more help with those now!

Reply

Submit reply

Register

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?

    this is what you'll be called on TSR

  2. this can't be left blank
    this email is already registered. Forgotten your password?

    never shared and never spammed

  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. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide the button to the right to create your account

    Slide to join now Processing…

Updated: April 9, 2012
New on TSR

Student crowdfunds degree

Graduate raises £26,000 online for Masters course

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