查看完整版本 : (急)又係物理問題少年問功課

terryxx14 2012-7-16 04:16 PM

(急)又係物理問題少年問功課

又有三題想麻煩CHING:loveliness::$
[attach]1881275[/attach]

14c14c 2012-7-16 05:48 PM

3. let the angle be x
Tcosx = mv^2/r
Tcosx = 50x(3.5^2)/2 = 1225/4-----(1)

Tsinx=mg
Tsinx=50g = 500 (if u take g=10) ----(2)

(2)/(1): tanx = 500/(1225/4)
x=58.51 in degree

terryxx14 2012-7-16 06:11 PM

Tcosx = 50x(3.5^2)/2 = 1225/4-----(1)
:smile_39:
點解Tcosx=1225/4 ???
我計到係306.25既???

14c14c 2012-7-16 06:34 PM

[quote]原帖由 [i]terryxx14[/i] 於 2012-7-16 06:11 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=335826643&ptid=19989757][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
Tcosx = 50x(3.5^2)/2 = 1225/4-----(1)
:smile_39:
點解Tcosx=1225/4 ???
我計到係306.25既??? [/quote]
因為1225/4=306.25:smile_30:

terryxx14 2012-7-16 06:35 PM

HAHA......:smile_27:
計到傻左= =

Zzlaz 2012-7-18 03:55 PM

竟然靜到這個地步... 出下手先.:smile_08:

4. y = 15 sin 8pi t  (not cos as cos 0 = 1)

b.

(10^6) /I2 =    (25)^2 / (10)^2  (inversely-square law)

then place I2 into the dB equation, I forgot. just remember sth like 10^-12 is present.

Q2

Rate = Ce -kt

ln Rate1 = ln C- kt1

ln Rate 1 - ln Rate 2 = -k (t1 - t2)  -k delta t

solve k , then t1/2 = ln2/k , finished.

terryxx14 2012-7-18 08:09 PM

多謝打救呀ching!!!!!!:smile_40::smile_24::smile_o12::smile_o06:



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14c14c 2012-7-18 08:53 PM

4.我計到 y=+ -0.15sin[(10pi x)/3]
姐係y= + -0.15sin[(8pi t)]
since x=2.4t

Zzlaz 2012-7-18 11:26 PM

Ya, y = 0.15 sin 8t seems better, unit of y should be m.
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