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  • 28-02-2014 12:38pm
    #1
    itgirl268
    Registered Users, Registered Users 2 Posts: 55 ✭✭


    just after starting maths 2 module in college and im really confused about how to calculate this A car traveling at a speed of 7 m/s applies its brakes. The brakes result in a constant deceleration of -7.5 m/s^2. How far does the car travel before it comes to a stop?
    if someone can just point e in the right direction? plz!!


Comments

  • #2
    Nappy
    Registered Users, Registered Users 2 Posts: 329 ✭✭Nappy


    u: initial speed
    v: final speed
    a: acceleration
    s: distance

    u= 7
    v=0
    a=-7.5

    v^2 = u^2 + 2as

    s= (v^2 - u^2)/2a

    s = (0 - 49)/-15

    s = 3.2666


  • #3
    itgirl268
    Registered Users, Registered Users 2 Posts: 55 ✭✭itgirl268


    thanks that makes alot of sense!!


  • #4
    Yakuza
    Registered Users, Registered Users 2 Posts: 5,141 ✭✭✭Yakuza


    Just to add, you can also find the distance from the time it takes to stop from the other two mechanics equations:
    s = ut + ½at²
    v = u+at

    If the car is going at 7m/s, and decelerates at 7.5 m/s², then it takes (7/7.5) seconds to stop. (v = 0, u = 7, a = -7.5)

    In that time it travels 7 * (7/7.5) + .05 * (-7.5) * (7/7.5)² metres (note the sign of a)
    Which is (as above), 3.266667 metres.


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