查看完整版本 : 從KE-T graph看acceleration

雲艾法比 2013-4-1 07:49 PM

從KE-T graph看acceleration

ANSWER係B,我睇左solution,都唔係好接受到,因為數學未教y=(constant)(x)^0.5既graph,唔知呢到既師兄有咩其它解法?thx:loveliness:
個solution係先將呢個直線既kt-t graph變做一個smaller slope既直v^2-t graph
即將y=(constant)(t)+0
變做y=(constant/0.5m)(t)
呢到我接受到
跟住solution將v^2-t graph變v-t graph
即將y=(constant/0.5m)(t)
變做y={(constant/0.5m)(t)}^0.5
跟住佢就話個vt graph既slope係decreasing,所以答案係B...
我唔係好接受到囉:smile_13:

雲艾法比 2013-4-1 07:51 PM

sorry唔記得調反岩個方向tim:smile_43:

dustbus 2013-4-1 08:50 PM

下點解ke升緊反而係deceleration?

定係佢向相反方向加速ja

dustbus 2013-4-1 09:04 PM

1開始KE=0,跟住仲decelerate???個唯一講法咪姐係向相反方向加速

雲艾法比 2013-4-1 09:24 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-1 21:04 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357294657&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
1開始KE=0,跟住仲decelerate???個唯一講法咪姐係向相反方向加速 [/quote]solution:
個vt graph係gum...即係first increase then decrease???

dustbus 2013-4-1 10:31 PM

有d唔明點樣得出v^2同t係linear關係

1/2mat^2=1/2mv^2
        at^2=v^2
點睇都係v^2同t^2有linear關係啦...

一係你等下龍哥上上水解答你:smile_30: :smile_30:

雲艾法比 2013-4-1 10:57 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-1 22:31 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357303080&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
有d唔明點樣得出v^2同t係linear關係

1/2mat^2=1/2mv^2
        at^2=v^2
點睇都係v^2同t^2有linear關係啦...

一係你等下龍哥上上水解答你:smile_30: :smile_30: [/quote]
初初我都唔明 但之後我諗  當a係constant時,ke against t同v^2 against t graph 先會係quadratic



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14c14c 2013-4-1 10:57 PM

let k be some positive constant such that kt=K.E.
then 2kt=mv^2
2kt/m=(ds/dt)^2
sqrt(2kt/m) = ds/dt (we may choose the direction s.t. ds/dt>0)
0.5sqrt(2k/m)t^(-1/2) = ds^2/dt^2 = acceleration = a which is decreasing as t increase

唔用微積分我唔識解:smile_43:

14c14c 2013-4-1 10:59 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-1 10:31 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357303080&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
有d唔明點樣得出v^2同t係linear關係

1/2mat^2=1/2mv^2
        at^2=v^2
點睇都係v^2同t^2有linear關係啦...

一係你等下龍哥上上水解答你:smile_30: :smile_30: [/quote]
根據幅圖, kt=K.E. for some positive constant k
(y=mx)

↗亢龍無悔↙ 2013-4-1 11:28 PM

第1,我接受到個solution嘅解法
第2,acceleration decreasing即係when t=0, a=5; when t=1, a=4; when t=3, a=3, etc,當然個decreasing not necessarily linear
第3,#8 did an excellent work
第4,而家啲小朋友,學左少少differentiation同integration就開始扮哂野,用呢啲野去做physics:smile_04: 想當年AL physics唯一用到differentiation同integration就只有proof F = -dU/dr 同charges in capacitor.但係而家都out哂c:smile_04::smile_04::smile_04:

[[i] 本帖最後由 ↗亢龍無悔↙ 於 2013-4-1 11:29 PM 編輯 [/i]]

14c14c 2013-4-2 12:55 AM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-4-1 11:28 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357309234&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
第1,我接受到個solution嘅解法
第2,acceleration decreasing即係when t=0, a=5; when t=1, a=4; when t=3, a=3, etc,當然個decreasing not necessarily linear
第3,#8 did an excellent work
第4,而家 ... [/quote]
無計, 我AL phy除左mechanics(姐係AL applied math)勉強搞得掂之外
EM, wave, matter..全部死晒, 最後直頭drop埋physics:smile_27:

作為一個數學人, 我淨係有足夠能力比到一個數學D既solution
亦都想比一D phy唔叻, 但係數學還可以既人知道原來有一個咁既alternative solution
畢竟用識左calculus之後做真係好方便, 亦都唔洗memorize咁多野:smile_40:

dustbus 2013-4-2 08:39 PM

[quote]原帖由 [i]14c14c[/i] 於 2013-4-1 10:59 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357306182&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

根據幅圖, kt=K.E. for some positive constant k
(y=mx) [/quote]
我係話v^2同T果個圖= =
明明計到v^2同t^2係linear- -:smile_27:

14c14c 2013-4-2 11:35 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-2 08:39 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357388663&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

我係話v^2同T果個圖= =
明明計到v^2同t^2係linear- -:smile_27: [/quote]
kt=0.5mv^2
(2k/m)t=v^2

you can see t and v^2 are linear
since k is positive constant, m is positive constant, (2k/m) is a positive constant:smile_44:

dustbus 2013-4-2 11:40 PM

:funk: :funk: :funk: thank you ching

Zzlaz 2013-4-3 08:44 PM

低能少少, SUB數方法。:smile_13:

雲艾法比 2013-4-4 12:28 AM

[quote]原帖由 [i]14c14c[/i] 於 2013-4-2 00:55 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=357317799&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

無計, 我AL phy除左mechanics(姐係AL applied math)勉強搞得掂之外
EM, wave, matter..全部死晒, 最後直頭drop埋physics:smile_27:

作為一個數學人, 我淨係有足夠能力比到一個數學D既solution亦都想比一D ph ... [/quote]thx咁多位師兄:loveliness:可惜我既唔係數學人,又唔係科學人:smile_39:而家希望靠狂爆phy chem econ練習,去進步

Zzlaz 2013-4-11 07:47 PM

當年我選PURE MATHS, 而家又比番哂老師.

當年讀書, 讀完考完, 得番幾多呢, 只係享受過程而矣

dustbus 2013-4-11 08:41 PM

pure math日常生活根本唔會用到:smile_27: :smile_27:

雲艾法比 2013-4-11 09:16 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-11 20:41 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=358219571&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
pure math日常生活根本唔會用到:smile_27: :smile_27: [/quote]dustbus師兄讀m1定m2?我m1

Zzlaz 2013-4-11 09:21 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-4-11 08:41 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=358219571&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
pure math日常生活根本唔會用到:smile_27: :smile_27: [/quote]
除左普通話, 英文,中文同數學之外,其他野生活上都唔會用到.

dustbus 2013-4-11 10:01 PM

[quote]原帖由 [i]Zzlaz[/i] 於 2013-4-11 09:21 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=358223014&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

除左普通話, 英文,中文同數學之外,其他野生活上都唔會用到. [/quote]

岩,phy都算apply到既,起碼去海公都知機動遊戲d原理- -

[quote]原帖由 [i]雲艾法比[/i] 於 2013-4-11 09:16 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=358222590&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
dustbus師兄讀m1定m2?我m1 [/quote]

我m2

darigold 2013-4-25 06:15 AM

其它唔講,問問題可唔可以專業少少啊。
影相就算了,轉一下都唔轉?

雲艾法比 2013-4-25 06:35 PM

[quote]原帖由 [i]darigold[/i] 於 2013-4-25 06:15 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=359479732&ptid=21702601][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
其它唔講,問問題可唔可以專業少少啊。
影相就算了,轉一下都唔轉? [/quote]Don't take it too serious.:loveliness:I'm sorry if I infuriated you.

37182456 2013-4-28 02:31 PM

ke係0.5mv?,v二次左線性上升,姐係話vt graph個v係條curve,係increasing with a decreasing rate,所以acceleration係decreasing



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查看完整版本: 從KE-T graph看acceleration