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雲艾法比 2013-4-25 06:48 PM

Momentum and Energy

Thank you for helping:loveliness:

↗亢龍無悔↙ 2013-4-25 07:35 PM

M g 4 = 2M g h
h = 2cm
This answer seems incorrect~

[[i] 本帖最後由 ↗亢龍無悔↙ 於 2013-4-25 07:36 PM 編輯 [/i]]

dustbus 2013-4-25 07:35 PM

其實你題目都打左momentum + energy
姐係都係2方面approach姐

一開波咪delta KE=delta PE
      1/2v^2=gh

搵V,再用番conservation of momentum

     m1u1=(m1+m2)v1,where m1=m2 and they stuck together,so they have same velocity


WA龍哥都秒殺左:smile_30:

雲艾法比 2013-4-25 07:58 PM

今朝睇極 solution 都唔明,睇完兩位師兄既cm之後突然睇得明:smile_14:
Here is the solution:
When the two masses stuck together,the total mass doubled.As momentum is conserved,the[color=#ff0000] kinetic energy E=p^2/2m is halved.[/color]
By conservation of energy E=mgh,the maximum height h was decreased by a factor of 4 to 1 cm.The answer is D.

紅句應該接受到吧,咁as KE is halved,即GPE gain is also halved,that is:
4mg/2=2mgh
h=1cm,as the solution stated

↗亢龍無悔↙ 2013-4-25 08:02 PM

接受到,因為AL physics有呢樣野 that's why I said my answer at #2 seems incorrect

dustbus 2013-4-25 08:09 PM

btw題外話

喱個system點樣整先算係SHM???
我依家都唔明咩係SHM:smile_27: :smile_27:

Zzlaz 2013-4-25 11:44 PM

energy is not conserved in this case la la...

雲艾法比 2013-4-26 04:51 PM

[quote]原帖由 [i]Zzlaz[/i] 於 2013-4-25 23:44 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=359565694&ptid=21816364][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
energy is not conserved in this case la la... [/quote]yes as it is inelastic collision.

Zzlaz 2013-4-26 06:19 PM

對物理學提起點興趣

可惜小弟已經遠離讀書年紀....:smile_38:

等25岁以MATURE STUDENT 方式再入大學...:smile_27:

dustbus 2013-4-26 09:15 PM

有志者鄧竟成:loveliness:

Zzlaz 2013-4-27 09:11 PM

我的記憶需要重建:smile_34:
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