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    Just going through the edexcel M2 spec and found a mention of this but can't find it in the heinemann book. can someone please explain.

    thanks in advance,

    MB
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    Work done (eg work done against friction) = Loss in Kinetic Energy - Gain in Potential Energy
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    (Original post by Indelible)
    Work done (eg work done against friction) = Loss in Kinetic Energy - Gain in Potential Energy
    Thanks - does this always include P.E. and should I check my results with newton equations of motion if I have time? can someone put up an example.

    MB
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    This is a VERY hard question: 16 marks in total, if you can do this your ready for anything!

    Particle P is projected from the point A up the line of greatest slope of a rough plane which is inclined at an angle beta (written as B from now on) to the horizontal where sinB=4/5. P is projected with speed 5.6ms^-1 and the coefficient of friction between P and the plane is 4/7

    Given that P comes to rest at the point B

    a) use the Work-Energy principle to show that the distance AB is 1.4m (10 marks)

    The particle then slides back down the plane

    b) Find correct to 2 significant figures, the speed of P when it returns to A (6 marks)

    Answers coming any minute now
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    ok so draw a label with R, (mu)R, mg, and the slope angled at B and distance AB = d

    Resolve perp to the plane: R = mgcosB (cosB = 3/5 using 345 triangle)
    so R = mg(3/5)
    (mu)R = (12/35)mg
    Work done against friction = loss in KE - gain in PE
    change in height (h) = dsinB
    so:
    (12/35)mgd = [0.5m(5.6)^2] - [mgdsinB] = 15.68 - (4/5)gd
    (40/35)gd = 0.5(5.6)^2
    d = 1.4

    part b coming soon
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    b) work done against friction = loss of KE (PE returns to normal due to no change in height)

    (12/35)mg(2d) = 0.5m(5.6^2 - v^2)
    1.92g =5.6^2 - v^2
    v^2 = 12.544
    v= 3.5ms^-1 (2sf)

    quite straight forward but remember to double the distance because it moves up and then back down the slope
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    Thanks, I think i've got it. I got the first part right already -I'll practice in the morning.

    MB
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    this is more like an M1 quaestion.
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    (Original post by musicboy)
    Just going through the edexcel M2 spec and found a mention of this but can't find it in the heinemann book. can someone please explain.

    thanks in advance,

    MB
    In case you want to take heat into consideration:

    delta U = Q - W

    Where delta U is the change in energy of the system, Q is the heat flowing into the system, and W is the work done by the system.
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    yeah, thanks for the questions, i got the first part right, although i think that the marks scheme is giving too many marks for it, although im not complaining.

    and the second part was kool. although i did it slightly different to you.

    i had the two forces, the friction and accelerative force due to gravity, and putting them into F=ma cancels the m's out so you get acceleration in terms of g and then use suvat to work out the speed after travelling 1.4m.
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    (Original post by lexazver203)
    this is more like an M1 quaestion.
    It would be M1 if you solved it with equations of motion (as you can) but it specifies work-energy and is thus M2.

    MB
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    (Original post by musicboy)
    It would be M1 if you solved it with equations of motion (as you can) but it specifies work-energy and is thus M2.

    MB
    But he still used a principle of resolving R perpendicullar to the plane, which is M1
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    OK - finally got my head round it - you are a real comrade. have some rep!

    MB
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    so? it also uses multiplication which is primary school work.
    All maths is a progresion using things youve learnt before.
    The question states you must use the work-energy principle so its M2
 
 
 
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