Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    3
    ReputationRep:
    A car moving at a velocity of 20ms^-1 brakes to a standstill in a distance of 40m. A child of mass 15kg is sitting in a forward-facing child car seat fitted to the back seat of the car.

    (c) Road accidents involving children are being reduced by reducing the speed limit near schools to 20 mph (9ms^-1). Discuss the effect this has on road safety where the speed limit is currently 30 mph.

    This question is 3 marks and I don't know what to write D: help pls
    • Aston Villa FC Supporter
    Offline

    3
    ReputationRep:
    Aston Villa FC Supporter
    (Original post by CookieHero)
    A car moving at a velocity of 20ms^-1 brakes to a standstill in a distance of 40m. A child of mass 15kg is sitting in a forward-facing child car seat fitted to the back seat of the car.

    (c) Road accidents involving children are being reduced by reducing the speed limit near schools to 20 mph (9ms^-1). Discuss the effect this has on road safety where the speed limit is currently 30 mph.

    This question is 3 marks and I don't know what to write D: help pls
    Think about what would happen if there was a crash. The deceleration would be greater the faster the initial velocity. So if you decrease the velocity, you decrease the deceleration (assuming same time for impact). Since F =ma, the slower the speed of the car, the smaller the force of the impact.
    • Study Helper
    Online

    21
    ReputationRep:
    Study Helper
    (Original post by CookieHero)
    A car moving at a velocity of 20ms^-1 brakes to a standstill in a distance of 40m. A child of mass 15kg is sitting in a forward-facing child car seat fitted to the back seat of the car.

    (c) Road accidents involving children are being reduced by reducing the speed limit near schools to 20 mph (9ms^-1). Discuss the effect this has on road safety where the speed limit is currently 30 mph.

    This question is 3 marks and I don't know what to write D: help pls
    Think about:

    The kinetic energy of the child inside the car.

    K.E. = \frac{1}{2}mv^2 and plug the values in to see that dropping the velocity by approximately half, reduces the energy involved by a factor of 4.

    i.e. the child is far more likely to survive the impact with less injury because he/she is hit with a substantially reduced force.

    Also consider:

    a) the stopping distance of the car (the questions hints at this by stating 40m). i.e. because the cars K.E. is one quarter at the lower speed, the car will stop in far less than half of 40m.

    b)consider also the reaction time of the driver to avoid the collision. The car will travel far less distance before the driver reacts to avoid the collision.
    • Thread Starter
    Offline

    3
    ReputationRep:
    Thanks for your help I get what to write now
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.