Recent content by I-need-help

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    Efficence - Calculate the Force needed to life this load

    Homework Statement Consider a mechanical car jack. To change a wheel it may need to lift a load of 2000N. Suppose that one rotation of the screw raises the car by 10mm. You apply a force to the end of the lever, 0.5m long, through a full circle. The jack is only 40% efficient. Calculate the...
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    Undergrad Further Maths, D1 - Dijkstra's Algorithm

    Hmmm, after looking at several past papers, it doesn't seem as if they would ask you anything like that. But be careful anyway, they do randomly throw related things in there.
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    Undergrad Further Maths, D1 - Dijkstra's Algorithm

    @willem2 Thank you for the reply! That makes so much sense to me now. Thanks
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    Summing Series (Sigma Notation)

    @HallsOfIvy Hmm thanks, for the help, I'll try to factorise those now, since the book wants it to be factorised.
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    Summing Series (Sigma Notation)

    Yeah ok, I've done that, but the textbook answers want it to be "factorised", and I'm unsure how to do that after subtracting... Thanks for your help.
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    Summing Series (Sigma Notation)

    Homework Statement a) n[SIZE="5"]Ʃ[SIZE="5"]r2(r-1)r=1 Homework Equations Using the summation series formulae... The Attempt at a Solution So far I have got: r2(r-1) = r3-r2 Ʃr3 = \frac{1}{4}n2 (n+1)2 Ʃr2 = \frac{1}{6}n(n+1)(2n+1) Therefore, Ʃr3-r2 = \frac{1}{4}n2...
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    Electrical Power - Equation Questions:

    Ah thanks again gneill!
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    Electrical Power - Equation Questions:

    Each cell will last... 2300mA shared by 120 mA ... so, 19.2 hours. And that's the right answer in the back of the book... wow. Hmm. Thanks! That is right isn't it? The textbook isn't always necessarily correct.
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    Electrical Power - Equation Questions:

    Ah yeah, missed out some info. The bulb is labelled 6.0 V and 120mA... no wattage, but you could work that out, so P = 6V x 0.12W = 0.72W
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    Electrical Power - Equation Questions:

    A 1.5V rechargeable cell is labelled 2300 mA h. This means that it can supply the equivalent of 2300 mA for one hour. b) How much energy does the cell store in: i- mWh? ii- J? and c) How long can four cells, connected in series, light the bulb? for b) i- I got: W = V x Q, so W = V x I...
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    The Effect of Temperature on Resistivity

    1) A thermistor is connected through a switch to a 12V power supply of negligible internal resistance. When the switch is closed, the initial current in the circuiy is 14mA. A few minutes later it has risen to a constant 20mA. Does the thermistor dissipate more power initially, or after it...
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    Undergrad Further Maths, D1 - Dijkstra's Algorithm

    Hi, I can do Dijkstra's Algorithm alright, but I always have problems with questions which have some relevance to the "Order of the Algorithm". For example, in the Further Maths, Decision 1 (OCR) textbook: 8) Suppose you purchase a new computer which is 100 times as fast as your old one...
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    Help Easy Physics - Resistivity Ratios

    Ahhhh okay, thanks so much for your help. Much appreciated. :)
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    Help Easy Physics - Resistivity Ratios

    Okay, thank you. I understand that, I'm just not sure how to get a ratio from that, with no other information... I'm not even sure if I need to work out a ratio actually. Oh well, thanks anyway.
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    Help Easy Physics - Resistivity Ratios

    The resistivity of Aluminium is twice that of copper. However, the density of Aluminium is one-third that of Copper. a) For equal length and resistance, calculate the ratio: mass of aluminium/mass of copperI'm thinking, the density ratio (Al:Cu) is 1:3 ...and the resistivity ratio is 2:1 ...so...