Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Stuck on this question. Any help appreciated. Calculate the force required to stop a 750 kg car which is travelling at 22 m/s if the crumple zone crumples by 70 centimetres. How do I work this out?
    Offline

    0
    ReputationRep:
    I assume "crumple zone" equates to the distance over which the car is slowed down.

    Start by using a suvat equation to find the acceleration. Use that in F=ma to find force.
    Offline

    0
    ReputationRep:
    NO NO NO! use Energy!
    • Thread Starter
    Offline

    2
    ReputationRep:
    And does increasing the weight of car affect the thinking distance?
    • Thread Starter
    Offline

    2
    ReputationRep:
    And how does increasing the weight of car affect the thinking distance?
    Offline

    9
    ReputationRep:
    Energy!!! Work out the kinetic energy of the car (1/2mv^2). This is equal to the work done in crumpling the crumple zone (force*distance)
    Edit: Does being in a heavy car make you think more slowly?

    Yes it does!!!!?!



    Wut?
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by running from demons)
    Energy!!! Work out the kinetic energy of the car (1/2mv^2). This is equal to the work done in crumpling the crumple zone (force*distance)
    Edit: Does being in a heavy car make you think more slowly?

    Yes it does!!!!?!



    Wut?
    So would it be 1/2 * 750 * 22 = f * 0.8
    but that means f = 10312.5 ??
    Offline

    8
    ReputationRep:
    Dont forget to square v.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by teachercol)
    Dont forget to square v.
    THanks so its 226875 Newtons.
    Offline

    0
    ReputationRep:
    I got 259286N

    v^2=u^2+2as

    0=484+1.4a

    -484=1.4a

    a=345.714286

    f=ma

    f=750*345.714286

    f=259286N
    • Thread Starter
    Offline

    2
    ReputationRep:
    Sorry. Last question. If I know the speed for the car, the driver's mass and therefore figure out the kinetic energy, how can I use energy transferred = average force * distance to find out the average force exerted by the seatbelt when energy is transferred to it due to stretching.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by shrep)
    I got 259286N

    v^2=u^2+2as

    0=484+1.4a

    -484=1.4a

    a=345.714286

    f=ma

    f=750*345.714286

    f=259286N
    THanks. I was using 0.8 instead of 0.7. Could you help with the question I posted above?
    Offline

    0
    ReputationRep:
    I'm guessing that ud use the distance that the seatbelt stretched as the distance in that question. Btw i know its quicker 2 use the KE in the first part but I cant get SUVAT out of my head thanks to M1 lol.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (Original post by shrep)
    I'm guessing that ud use the distance that the seatbelt stretched as the distance in that question. Btw i know its quicker 2 use the KE in the first part but I cant get SUVAT out of my head thanks to M1 lol.
    This is a spearate question though and there is no distance given which is why Im stuck
    Offline

    0
    ReputationRep:
    Well then i guess u assume his acceleration is the same as the car/the distance is the same. So just change the mass of the car to the mass of the driver.
    Offline

    11
    ReputationRep:
    (Original post by D-Day)
    I assume "crumple zone" equates to the distance over which the car is slowed down.

    Start by using a suvat equation to find the acceleration. Use that in F=ma to find force.
    "crumple zone" , "thinking distance" , sounds like a terribly vague GCSE "science" questions.That would be a pretty poor assumption but it's the only one you can really make given the info in the question.
    Offline

    8
    ReputationRep:
    Its AS Physics
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: November 12, 2008
Poll
Do you think parents should charge rent?

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

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