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    I'm stuck on two questions within the topic of kinematics of a particle any help would really be appreciated.
    8. A Ball is thrown vertically upwards with a speed of 15 metres per second from a point 1m above the ground. Find the speed with which it hits the floor. If it rebounds with a speed which is half the speed with which it hits the floor, find its greatest height after the first bounce.
    9. A particle is projected upwards with a speed of 14 meters per second. Find for how long it is above 2m.
    I have no idea where to start please help ASAP.
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    8) using SUVAT:
    S= -1 since it is going to be moving down 1 meter
    U= 15
    A= -9.8
    and we are trying to find V, the speed at which it hits the floor. using v^2=u^2+2as:
    v^2=15^2+2(-9.8)(-1)
    v^2=244.1
    v=15.64 m/s

    Then using SUVAT again the find it's greatest height on the second bounce
    U = 7.82 half of the speed at which it hits the ground
    A = -9.8
    V = 0
    and we are trying to find S, we can use v^2=u^2+2as
    0=7.82^2+2(-9.8)(s)
    0=61.15 - 19.6s
    19.6s = 61.15
    s = 3.12 m

    9) First find the speed of the particle once it is 2m above the ground:
    S = 2
    U = 14
    A = -9.8

    V^2=U^2 + 2as
    v^2 = 14^2 + 2(-9.8)(2)
    v^2 = 156.8
    v = 12.52m/s

    Then find the time it takes to get from 2m to it's max. height
    U = 12.52
    V = 0
    A = -9.8

    V=U+AT
    0=12.52-9.8t
    9.8t=12,52
    t=1.27s

    since this is the time it takes to get from 2m to it's max height, multiply by 2 to get the total time above 2m

    1.27 x 2 = 2.56s
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    (Original post by liam3781)
    8) using SUVAT:
    Giving full solutions isn't very helpful to the OP - you won't be there in the exam so in future try to give hints to allow them to work through it on their own, rather than just posting the answers
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    (Original post by fiimarie)
    I'm stuck on two questions within the topic of kinematics of a particle any help would really be appreciated.
    8. A Ball is thrown vertically upwards with a speed of 15 metres per second from a point 1m above the ground. Find the speed with which it hits the floor. If it rebounds with a speed which is half the speed with which it hits the floor, find its greatest height after the first bounce.
    9. A particle is projected upwards with a speed of 14 meters per second. Find for how long it is above 2m.
    I have no idea where to start please help ASAP.
    As a general rule with Mechanics, always draw a diagram first with all of the information. It usually helps a lot and becomes clear what you need to do
 
 
 

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