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    A test is carried out on a rocket, of mass 200kg, which is fired horizontally at a speed 50m p/s. The rocket experiences a constant air resistance force of 1568 N. It travels a distance of 108m before it hits a stationary tank, of mass 4800kg. Assume the rocket always travels horizontally.

    a) Find the speed of the rocket when it has travelled a distance of 108m.

    When the rocket hits the tank it becomes lodged into it:

    b) Find the speed of the tank and the rocket just after the collision ( i can probably do this with the conservation of momentum, but i need part a) to do it!)

    The tank then slides until it comes to rest. The coefficient of friction is 0.6 between the tank and the ground. Neglect air resistance.

    c) find the distance that the tank slides.

    Any help would be much appreciated, have got M1 exam tomorrow, and everything was going well....until now... :confused:
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    a)
    Two ways of doing it. I'll do the simplier longer way first.
    F= ma
    a = 1568/200 = 7.84ms-2
    v^2 = u^2 + 2as
    Since a is in the opposite direction to s a is negative.
    v^2 = 50^2 +2 x 108 x -7.84
    v^2 = 2500 - 1693.44
    v^2 = 806.56
    v = 28.4ms-1

    Alternatively
    E = Fs
    1/2mv^2 = E
    1/2mv^2 = 1/2mu^2 - Fs
    v^2 = u^2 - 2Fs/m
    Which gives the same equation as above.

    b) Assume inelastic collision.
    200u = (200+4800)v
    v = 200 x 28.4/5000
    v = 1.136m/s

    c) F = mju R
    Assume the rocket becomes part of the tank, hence R = 5000g
    F = ma
    ma = mju m g
    a = mju g (hmm...mju g....that shop...OooO)
    v^2 = u^2 + 2as
    0 = u^2 +2as
    2 mju g s = u^2
    s = 1/2 u^2 /mju /g
    s = 0.1096m
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    ahh, thanks, i just wasnt sure whether a = 1568/200 or whether there was another force driving the rocket forwards, ie whether F - 1568 = 200a, or as you said 1568 = 200a.

    Thanks for clearing that up - did you just realise there was no other force acting other than the air resistance, how did you know that? This always confuses me, how is the rocket moving forwards then? if theres no force going forwards, only one going backwards? Thanks for you help! x
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    Mr = 200 kg
    Mt = 4,800 kg
    u = 50 m/s
    R =1568 N

    a)
    R = Mr*d
    d = 1568/200
    d = 7.84 m/s²
    ===========

    v² - u² = 2as
    v² - 50² = -2*7.84*108
    v² = 2500 - 1693.44
    v² = 806.56
    v = 28.4 m/s
    ==========

    b)
    Mr.v = (Mr + Mt)v'
    v' = (200*2.84) / (200 + 4800) = 200*28.4/5000
    v' = 1.136 m/s
    ===========

    c)
    Neglecting air resistence,

    Fr = µ.NR = 0.6*5000*g = 29,400 N

    Fr = (5000)*d2
    d2 = 29,400/5000 = 5.88 m/s²

    v² - u² = 2as
    s = 1.136²/(2*5.88)
    s = 0.1097 m
    s = 11 cm
    ========
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    (Original post by xXxKatiexXx)
    ahh, thanks, i just wasnt sure whether a = 1568/200 or whether there was another force driving the rocket forwards, ie whether F - 1568 = 200a, or as you said 1568 = 200a.

    Thanks for clearing that up - did you just realise there was no other force acting other than the air resistance, how did you know that? This always confuses me, how is the rocket moving forwards then? if theres no force going forwards, only one going backwards? Thanks for you help! x
    This is a created situation.
    A rocket is (somehow) given a speed of 50 m/s.
    Your also told that the rocket travels horizontally. (which doesn't happen in practice) This is just to simplify thngs..

    You're not told in the question that there is any other force acting, so assume none.
    Assume that the rocket has a constant speed, that there is no propulsive force (none mentioned), and a constant resistence slowing it down from the starting speed.

    Your problem is then to figure out what happens afterwards

    Always watch out for gravity effects though! That means a force is acting.
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    thanks everyone - i think i was just making everything much more complicated than it needed to be! Wish me luck!
 
 
 
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