# 查看完整版本 : projectile motion

startanew 2013-11-2 04:09 PM

## projectile motion

[img]http://i1163.photobucket.com/albums/q554/startanewww/projectilemotion1.png[/img]

[img]http://i1163.photobucket.com/albums/q554/startanewww/projectilemotion2-1.png[/img]

Thanks!

[[i] 本帖最後由 startanew 於 2013-11-2 05:07 PM 編輯 [/i]]

↗亢龍無悔↙ 2013-11-2 04:24 PM

[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

startanew 2013-11-2 04:29 PM

7cos15/v = cos θ
wrong?

↗亢龍無悔↙ 2013-11-2 05:28 PM

[quote]原帖由 [i]startanew[/i] 於 2-11-2013 04:29 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374908134&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
7cos15/v = cos θ
wrong? [/quote] 仲覺得無問題？

dustbus 2013-11-2 06:12 PM

cos係計vertical定horizontal既speed

startanew 2013-11-2 07:26 PM

2b) vertical distance: 1/2 (9.81)(0.8)^2 = 3.14 m
(3.14)(9.81) + 1/2 (7)^2 = 1/2 v^2
v = 10.5 ms^(-1)
Ux / v = cos θ
θ = 50.0

startanew 2013-11-2 07:26 PM

ans: θ = 41.8

[[i] 本帖最後由 startanew 於 2013-11-4 05:31 PM 編輯 [/i]]

↗亢龍無悔↙ 2013-11-2 08:27 PM

[quote]原帖由 [i]startanew[/i] 於 2-11-2013 07:26 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374917155&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]ans: θ = 41.8答案係用 Vy/Vx = tan θ但點解我咁做就唔岩? [/quote]返去form 2重學trigonometry 啦:smile_04:

[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

dustbus 2013-11-2 09:11 PM

[quote]原帖由 [i]startanew[/i] 於 2013-11-2 07:26 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374917117&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

2b) vertical distance: 1/2 (9.81)(0.8)^2 = 3.14 m
(3.14)(9.81) + 1/2 (7)^2 = 1/2 v^2
v = 10.5 ms^(-1)
Ux / v = cos θ
θ = 50.0 [/quote]

startanew 2013-11-2 09:31 PM

vertical distance: s = 7sin15 (0.8) - 1/2 g (0.8)^2 = -1.6898 m
(1.6898)(9.81) + 1/2 7^2 = 1/2 v^2
v = 9.06 ms^(-1)
7cos15/9.06 = cos θ
θ = 41.8

dustbus 2013-11-3 12:20 PM

LOL:smile_30: :smile_30: :smile_30: :smile_30:

startanew 2013-11-3 12:56 PM

## 回覆 11# 的帖子

:smile_o08:

dustbus 2013-11-3 08:48 PM

:smile_30: :smile_30: 冇野了你做得很好

↗亢龍無悔↙ 2013-11-4 08:34 AM

[quote]原帖由 [i]startanew[/i] 於 2-11-2013 09:31 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374923838&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]我唔明你地咩事要咁講我.......我自己睇多次, 發現我只係vertical distance計錯, cos冇用錯囉!!!!!!!!!!!!!!!!!!!!!!!!! :smile_o03:  :') vertical distance: s = 7sin15 (0.8) - 1/2 g (0.8)^2 = -1.6898 m ... [/quote]最尾個cos angle 岩咩？

[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

startanew 2013-11-4 01:12 PM

#7
ans: 41.8

You still think I'm wrong? = =
:smile_o08: :smile_o02:

startanew 2013-11-4 01:14 PM

Although the method I use is slow, it is correct!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
:Q

↗亢龍無悔↙ 2013-11-4 02:52 PM

[quote]原帖由 [i]startanew[/i] 於 4-11-2013 01:12 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=375035360&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]#7ans: 41.8You still think I'm wrong? = =:smile_o08: :smile_o02: [/quote]你之前用紅字果到明明係用cos ，幾時變左tan ?

“7cos15/9.06 = cos θ”

[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

[[i] 本帖最後由 ↗亢龍無悔↙ 於 2013-11-4 02:57 PM 使用[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg [/img][/url] 編輯 [/i]]

startanew 2013-11-4 05:29 PM

#7 我本來就係打 Vy/Vx = tan θ
"[b][color=#ff0000]vertical distance / horizontal distance[/color][/b] = tan θ" <-- 我搞錯左, 呢個係做第3題既方法

[quote]我就係見你vertical , horizontal component combine一齊用cos 我先直接話你錯[/quote]
#6 我已經好清楚咁話你知我用緊 Ux / [b]resultant v[/b] = cos θ

[quote]仲有#6果到，點唔一開始就用v=u+at呢？[/quote]

startanew 2013-11-4 05:32 PM

#1 1/2 u^2 + gh = 1/2 v^2 都係.............

[[i] 本帖最後由 startanew 於 2013-11-4 05:33 PM 編輯 [/i]]

↗亢龍無悔↙ 2013-11-4 06:14 PM

7cos15 係horizontal, 9.06係vertical , 有咩理由個angle 係arc cos去搵[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

[[i] 本帖最後由 ↗亢龍無悔↙ 於 2013-11-4 06:16 PM 使用[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg [/img][/url] 編輯 [/i]]

startanew 2013-11-4 06:20 PM

## 回覆 20# 的帖子

startanew 2013-11-4 06:22 PM

[[i] 本帖最後由 startanew 於 2013-11-4 06:24 PM 編輯 [/i]]

startanew 2013-11-4 06:22 PM

startanew 2013-11-4 06:39 PM

(全部用最準既數)

↗亢龍無悔↙ 2013-11-4 06:45 PM

[url=http://www.discuss.com.hk/android][img=100,23]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img][/url]

startanew 2013-11-4 06:53 PM

## 回覆 25# 的帖子

↗亢龍無悔↙ 2013-11-4 07:30 PM

## 回覆 26# 的帖子

#21唔講9.06 係 resultant, 我都仲會以為係 vertical component

startanew 2013-11-4 07:46 PM

#1 1/2 u^2 + gh = 1/2 v^2 如果你有認真睇既話就唔會誤會......

ok 下次我 show steps 會加多幾隻字...
:smile_o08:

dustbus 2013-11-4 07:51 PM

[quote]原帖由 [i]startanew[/i] 於 2013-11-4 06:22 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=375052354&ptid=22627106][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

startanew 2013-11-4 08:47 PM

"如果你叫佢學番D mechanics

:smile_o16: