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    A red snooker ball that was at rest is hit directly by a white ball moving at 0.8ms-1 after the collision the red ball moves at 0.75ms-1. Find the speed of the white ball after the collision, assuming the momentum is conserved. State clearly any further assumption you have made.
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    are they in a straight line, or is it an oblique impact?
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    It doesnt say, although the first part of the question says:

    list four factors that could influence the outcome of a collisions between 2 snooker balls that are rollong along a straight line towards each other.
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    (Original post by imasillynarb)
    A red snooker ball that was at rest is hit directly by a white ball moving at 0.8ms-1 after the collision the red ball moves at 0.75ms-1. Find the speed of the white ball after the collision, assuming the momentum is conserved. State clearly any further assumption you have made.
    assuming:
    1) they are in a straight line
    2) their masses are equal
    3) it is an elastic collision

    0.8 + 0 = v + 0.75

    v = 0.05 m/s
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    Ahh yeh, the whole mass is equal thing. What about this one:

    A trck A of mass 15 tonnes moves along a straight railway line with a speed of 8ms-1. It colldies with a truck B of mass 10 tonnes which is moving with a speed of 4ms-1 along the same line and in the same direction. During the collision the impulse acting on each truck has magnitude 30000Ns. Calculate the speed of truck A and B immediately after the collision and the total loss of kinetic energy due to the collision.

    I got 7 and 10 ms-1 which is clearly wrong as it cant of sped up surely?
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    (Original post by imasillynarb)
    I got 7 and 10 ms-1 which is clearly wrong as it cant of sped up surely?
    it can speed up. consider a 15 tonne truck hitting a grain of rice. the grain of rice will speed up a lot. it depends on the masses. generally, if a large mass hits a small mass, the small mass will speed up quite a bit, and the large mass will decelerate a small bit.
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    (Original post by elpaw)
    it can speed up. consider a 15 tonne truck hitting a grain of rice. the grain of rice will speed up a lot. it depends on the masses. generally, if a large mass hits a small mass, the small mass will speed up quite a bit, and the large mass will decelerate a small bit.
    The combined speeds before = 12ms-1 combined speeds after = 17ms-1 ...cant of done that surely?
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    (Original post by imasillynarb)
    A red snooker ball that was at rest is hit directly by a white ball moving at 0.8ms-1 after the collision the red ball moves at 0.75ms-1. Find the speed of the white ball after the collision, assuming the momentum is conserved. State clearly any further assumption you have made.
    It depends whether there was a "kick" when the balls made contact - i.e.) fricition due to excess deposited chalk.

    This would otherwise slow down the speed of the white ball after the collision.
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    (Original post by bono)
    It depends whether there was a "kick" when the balls made contact - i.e.) fricition due to excess deposited chalk.

    This would otherwise slow down the speed of the white ball after the collision.
    Serious help only please, I have to be up in 6 hours.
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    (Original post by imasillynarb)
    Serious help only please, I have to be up in 6 hours.
    Sorry.
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    (Original post by imasillynarb)
    The combined speeds before = 12ms-1 combined speeds after = 17ms-1 ...cant of done that surely?
    15*8² + 10*4² = 1120
    15*7² + 10*10² = 1240

    OK that's impossible from an energy point of view, in the current situation.

    but it is generally possible. think about a truck hitting an atom. the truck will carry on with a similar speed, but the atom could go off at a few hundred m/s. the speeds after are much greater than the speeds before. so it is possible.

    but in your case, you have made a mistake somewhere, because the energy has increased, which shouldnt be the case.
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    (Original post by elpaw)
    assuming:
    1) they are in a straight line
    2) their masses are equal
    3) it is an elastic collision

    0.8 + 0 = v + 0.75

    v = 0.05 m/s
    ms^-1 is more appropriate
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    (Original post by elpaw)
    15*8² + 10*4² = 1120
    15*7² + 10*10² = 1240

    OK that's impossible from an energy point of view, in the current situation.

    but it is generally possible. think about a truck hitting an atom. the truck will carry on with a similar speed, but the atom could go off at a few hundred m/s. the speeds after are much greater than the speeds before. so it is possible.

    but in your case, you have made a mistake somewhere, because the energy has increased, which shouldnt be the case.
    I dont understand where the mistake is, thats my point.
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    (Original post by bono)
    ms^-1 is more appropriate
    why is it more appropriate?
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    (Original post by elpaw)
    why is it more appropriate?
    My teacher said so?
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    5.2 and 7.2ms-1, how does that sound?
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    (Original post by imasillynarb)
    Ahh yeh, the whole mass is equal thing. What about this one:

    A trck A of mass 15 tonnes moves along a straight railway line with a speed of 8ms-1. It colldies with a truck B of mass 10 tonnes which is moving with a speed of 4ms-1 along the same line and in the same direction. During the collision the impulse acting on each truck has magnitude 30000Ns. Calculate the speed of truck A and B immediately after the collision and the total loss of kinetic energy due to the collision.

    I got 7 and 10 ms-1 which is clearly wrong as it cant of sped up surely?
    15000*8+10000*4 = 160000

    15000A + 10000B = 160000 - 30000 = 150000

    A = 5.2
    B = 7.2
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    (Original post by imasillynarb)
    5.2 and 7.2ms-1, how does that sound?
    that sounds good, because the energy goes down, so it's OK
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    (Original post by elpaw)
    that sounds good, because the energy goes down, so it's OK
    I got B = 5.2 and A = 7.2 though, not the other way round :/
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    (Original post by imasillynarb)
    I got B = 5.2 and A = 7.2 though, not the other way round :/
    oh well, i didnt do the complete solution, i saw your answers and put them in, because they sound right.
 
 
 
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