香港寵物小精靈村落 論壇

標題: phy~從不知怎麼是對的 [打印本頁]

---

作者: 小霞的fans    時間: 26/2/2010 11:16 AM
標題: phy~從不知怎麼是對的
1.the motion of a toy car is recorded by a ticket-tape tine with a frequency of　　
100Hz.the distance between the first two successive dots and the final two successive dots is 1cm and 7cm respectively.also,there are 5 dots on the tape.

find the initial velocity,final velocity and hence the acceleration of the toy car.

initial velocity 應該係1/1/100 =100cms^-1
final 應該係 7/1/100 = 700cms^-1

acceleration係 7ms^-1  - 1ms^-1/ time
個time應該係幾多.. 唔識搵個時間.. 果2個velocity既時間係幾多...?


2.如個1舊石頭被氣球條線縛住,,慢慢由地下升上空中
如果向上係positive
姐係石頭上面既tension既magnitude大過weight既magnitude.
咁佢個acceleration係acceleration due to gravity=10ms^-2 ?
咁佢係向上加速定向上減速...?搞唔清楚呢個問題..好似加又好似減- - " thx

---

作者: 鴨    時間: 26/2/2010 02:28 PM


第一題時間是有給提示的
the motion of a toy car is recorded by a ticket-tape tine witha frequency of　　
100Hz.the distance between the first two successive dots and the final two successive dots is 1cm and 7cm respectively.also,there are 5 dots on the tape.

既然向上為positive
acceleration due to gravity必為-10ms^-2
但是acceleration due to gravity大多是在free fall 情況下才會用的
因這個代表的是W=mg的g
所以其實在計net force的時候你已經把其考慮在內
一般有剩力的acceleration是由net force來計的

---

作者: 小霞的fans    時間: 26/2/2010 04:47 PM

第一題時間是有給提示的
the motion of a toy car is recorded by a ticket-tape tine with a frequency of　　
100Hz.the distance between the first two successive dots and the final two successive dots is ...
RX78-2 發表於 25/2/2010 06:28 PM

                               
登錄/註冊後可看大圖

thx你...
第1題唔知點解時間係0.03s
tine for 1 dot應該係1/100=0.01s
由於5個dots之間有4個空位..咁應該係0.01x4 = 0.04 s ??
點解少左0.01s ..??

第2題,,其實佢係得1個acceleration (10ms^-2)
定係2個(T-mg=ma)
姐係佢係向上加速定減速t^t

---

作者: hk56740    時間: 26/2/2010 10:03 PM
2. take upward direction as positive.
let the mass of stone be m kg, T N be the tension between the stone and the string, the acceleration of stone be A m/s^2.
Weight of stone=mg
                     =m(-10)
                     =-10m N
Apply F=ma(Newton's Second Law),
T-(-10m)=mA
T+10m=mA

其實你要留意既係1個叫accelerationdue to gravity,另1個叫acceleration.
Weight係地球拉個object既力,=mass of object x acceleration due to gravity所以有需要包括埋用黎計net force.而acceleration係真實中個net force引致既加速.

---

作者: orb    時間: 27/2/2010 10:51 AM
Tension
↑
Ｏ    (Stone)
↓
mg


考量free body diagram, 就是如上
只要tension大過mg, stone永遠都向上加速
(tesion=mg, no acceletarion for stone: 原本向上升的繼續向上升)
(tension<mg, 連氣球一起向下拖)

---

作者: 小霞的fans    時間: 27/2/2010 02:40 PM
第2題明左啦謝謝~~

問另外1題似第1題的東東..

                               
登錄/註冊後可看大圖

an experiment is set up th find the acceleration due to gravity g on metal ball M.the ticket time-tape timer produces 50 dots per second.the above figure shows a paper tape obtained from the experiment.

1.find the time interval represented by AB.
ans:1/50x5=0.1s

2.find the average speed of the metal ball M during the time interval represented by part of strip
1.between A and B
2.between C and D
ans:1.u=0.132/0.1=1.32ms^-1
       2.v=0.318/0.1=3.18ms^-1

我的問題1:點解AB果段時間既速度係u唔係v ? direction of paper tape唔係由左去右?點解調轉左?

3.hence,find the value of g from the experiment
ans:g=3.18-1.32/0.2 =9.3ms^-2

我的問題2:點解個t係0.2唔係0.3 ? A同B之間係0.1s..C同D之間係0.1s..B同C之間都有0.1s架喎‥‥點解會係0.2既??

---

作者: 小霞的fans    時間: 2/3/2010 09:32 AM


另外再想問一問..
wave length of visible violet light in glass is greater than that in air.

我睇哂成本書都搵唔到有關資料..
點樣先知佢
wave length同speed既轉變呢 -  -?

同埋呢,,electromagnetic wave唔係係vacuum既speed先係3x10^8ms-1架咩?
點解係空氣度都係相同speed架?空氣唔係應該各有不同架咩-.-?
咁點解the speeds of electromagnetic waves are equal to the speed of light呢句說話係岩??

---

作者: 小霞的fans    時間: 31/3/2010 11:59 AM
又有新問題啦~...

A small metal ball of mass 4kg is dropped from rest tnto a sand pit.it is initally at a height of h=1.8m above surface of the sand.as it hits the sand,it moves further over a distance of s=0.2m before it stops.find the average force acting on the ball by the sand.

4x10x1.8=F(0.2)
F=360N
但我唔明點解答案係400N ,, 點解要加埋weight呢? weight應該係gravity比個ball既力黎架喎..而家唔係搵sand比佢既力架咩??

---

作者: Requiem    時間: 31/3/2010 12:12 PM

又有新問題啦~...

A small metal ball of mass 4kg is dropped from rest tnto a sand pit.it is initally at a height of h=1.8m above surface of the sand.as it hits the sand,it moves further over a dista ...
小霞的fans 發表於 31/3/2010 11:59 AM

                               
登錄/註冊後可看大圖

Net force acting on the ball=360N
The small metal ball still experiences gravity during its deceleration.
Hence, net force acting on the ball=force exerted on the ball by the sand-weight of the ball.

---

作者: 小霞的fans    時間: 31/3/2010 12:58 PM

Net force acting on the ball=360N
The small metal ball still experiences gravity during its deceleration.
Hence, net force acting on the ball=force exerted on the ball by the sand-weight of the  ...
Requiem 發表於 30/3/2010 04:12 PM

                               
登錄/註冊後可看大圖

force exerted on the ball by the sand係向上定向下既力?
如果係向上..呢個力大過weight..咁個波唔係向上運動咩?
佢仲向下行??
如果係向下既力..姐係同weight平行?? 唔係好明act係ball既力

---

作者: Requiem    時間: 31/3/2010 02:46 PM

force exerted on the ball by the sand係向上定向下既力?
如果係向上..呢個力大過weight..咁個波唔係向上運動咩?
佢仲向下行??
如果係向下既力..姐係同weight平行?? 唔係好明act係ball既力
小霞的fans 發表於 31/3/2010 12:58 PM

                               
登錄/註冊後可看大圖

force exerted on the ball by the sand是向上的力。
Motion不一定跟Net force同方向的，跟Net force同方向的是acceleration。
所以向上的net force會使原本velocity向下的波decelerate。

---

作者: 小霞的fans    時間: 31/3/2010 03:07 PM

force exerted on the ball by the sand是向上的力。
Motion不一定跟Net force同方向的，跟Net force同方向的是acceleration。
所以向上的net force會使原本velocity向下的波decelerate。
Requiem 發表於 30/3/2010 06:46 PM

                               
登錄/註冊後可看大圖

喔我明白啦...

                               
登錄/註冊後可看大圖

最左邊果個點係一個man ..he is in front of the mirror.我想問佢點解見到objectIII既..
同塊鏡平行都睇到=.=?

---

作者: PA    時間: 31/3/2010 04:06 PM

喔我明白啦...

http://i554.photobucket.com/albums/jj423/cheukkan3b39/af258b44.jpg

最左邊果個點係一個man ..he is in front of the mirror.我想問佢點解見到objectIII既..
同塊鏡平行都睇到=.=?
小霞的fans 發表於 31/3/2010 03:07 PM

                               
登錄/註冊後可看大圖

這題我做過，不過那幅圖是很明顯那個man是可以直接看到III的...不需要鏡的反射

                               
登錄/註冊後可看大圖

---

作者: 小霞的fans    時間: 31/3/2010 04:57 PM

這題我做過，不過那幅圖是很明顯那個man是可以直接看到III的...不需要鏡的反射

                               
登錄/註冊後可看大圖

木守宮的蛙糧-PA 發表於 30/3/2010 08:06 PM

                               
登錄/註冊後可看大圖

竟然係咁...唔該哂^^

                               
登錄/註冊後可看大圖

呢d 作用與反作用呢..我搞唔清....
架trolley我唔知佢幾時郁幾時唔郁- - "" 希望有人詳細解比我聽.. thx x100000

---

作者: Requiem    時間: 31/3/2010 11:37 PM
冇CARDBOARD時:
System的風扇比力空氣向後流動，空氣比reaction force比成個system向右
情況類似兩個人企喺TROLLEY上互相推對方

有CARDBOARD時:
System的風扇比力空氣向後流動，空氣比reaction force比成個system向右
空氣撞上CARDBOARD，SYSTEM的CARDBOARD比力空氣，空氣會比番reaction force比成個system向左
=>BALANCE OF FORCE ON THE SYSTEM

唔知有冇錯(?)

---

作者: unlock-YM    時間: 1/4/2010 01:07 AM
不如將個問題現實化少少(我比較鍾意咁做MC lol) :
你成個人訓係地下豎起膝頭，你用手推隻腳咁你會唔會成個人向前??道理係一樣的。

---

作者: 小霞的fans    時間: 1/4/2010 10:20 AM

冇CARDBOARD時:
System的風扇比力空氣向後流動，空氣比reaction force比成個system向右
情況類似兩個人企喺TROLLEY上互相推對方

有CARDBOARD時:
System的風扇比力空氣向後流動，空氣比reaction force比成 ...
Requiem 發表於 31/3/2010 03:37 AM

                               
登錄/註冊後可看大圖

空氣撞上CARDBOARD，SYSTEM的CARDBOARD比力空氣，空氣會比番reaction force比成個system向左

呢度唔係幾明..空氣向後流動唔係比個左力cardboard!?咁cardboard應該比返個向右既力空氣?我搞錯左d咩><""唔該哂

---

作者: 小霞的fans    時間: 3/4/2010 02:47 PM
另外有1條問題..

An object slides down a sooth plane from rest.which of the following graphs shows the variation of kinetic energy with time.
我唔係問個graph,..係問d step..
K.E.=1/2mv^2  by v=u+at
      =1/2m(u+at)^2
      =1/2ma^2t^2
since 1/2ma^2 is constant,,K.E. varies with t^2

我想問下點解a^2會係constant = ="" thx~~ 我呢方面好弱..

---

作者: unlock-YM    時間: 3/4/2010 03:15 PM

另外有1條問題..

An object slides down a sooth plane from rest.which of the following graphs shows the variation of kinetic energy with time.
我唔係問個graph,..係問d step..
K.E.=1/2mv^2  by v=u+at ...
小霞的fans 發表於 3/4/2010 02:47 PM

                               
登錄/註冊後可看大圖

因為m係constant，而a亦只係同g有關。

---

作者: 小霞的fans    時間: 3/4/2010 07:16 PM

因為m係constant，而a亦只係同g有關。
unlock-YM 發表於 2/4/2010 07:15 PM

                               
登錄/註冊後可看大圖

咁有咩時候a唔係constant架??(cert level黎講)
好似冇乜!?

---

作者: unlock-YM    時間: 3/4/2010 07:49 PM

咁有咩時候a唔係constant架??(cert level黎講)
好似冇乜!?
小霞的fans 發表於 3/4/2010 07:16 PM

                               
登錄/註冊後可看大圖

應該係冇。

---

作者: 小霞的fans    時間: 5/4/2010 10:54 AM


問題:
      一 一 一
A   l             l  C
___l             l___

A train of progressive waves travels from left to right.A同C區既深度係一樣...我想問點解A同C個wave form會唔一樣既~?唔係應該相同架咩?答案果度印呢..C區既wave既wavelength同A區一樣..不過C區個wave既高度短D..冇A區咁高..我想知點解-0-""
'

---

作者: [GW]赤沙    時間: 5/4/2010 12:26 PM

問題:
      一 一 一
A   l             l  C
___l             l___

A train of progressive waves travels from left to right.A同C區既深度係一樣...我想問點解A同C個wave form會唔一樣既~?唔係應該相同架 ...
小霞的fans 發表於 5/4/2010 10:54 AM

                               
登錄/註冊後可看大圖

高度 = Amplitude
而Amplitude的大小代表wave process的energy
Wave随着propagation, energy 下降, Amplitude 所以 gradually decrease.
但Amplitude 應該同wave form 無關 ...?

---

作者: 小霞的fans    時間: 13/4/2010 11:44 AM

高度 = Amplitude
而Amplitude的大小代表wave process的energy
Wave随着propagation, energy 下降, Amplitude 所以 gradually decrease.
但Amplitude 應該同wave form 無關 ...?
赤沙 發表於 4/4/2010 04:26 PM

                               
登錄/註冊後可看大圖

咁我想問問diffraction,,reflection 會唔會有energy loss架!?
佢地既amplitude都會gradually decrease?? thanks~

---

作者: inthomaspy    時間: 15/4/2010 01:04 AM

咁我想問問diffraction,,reflection 會唔會有energy loss架!?
佢地既amplitude都會gradually decrease?? thanks~
小霞的fans 發表於 13/4/2010 11:44 AM

                               
登錄/註冊後可看大圖

During reflection, there should have no energy loss
During diffraction, there will also have no energy loss but it leads to change in direction of wave propagation and re-distribution of energy. That is, some energy in the original wave are distributed to the 'bended' side of the diffracted wave.
  ︱             \        << some original energy is distributed here
  ︱             ︱
  ︱             ︱
  ︱             ︱
  ︱             /        << some original energy is distributed here
The amplitude of the wave will decrease gradually as it travels because there will be resistance and hence energy is lost to the surrounding

---

作者: 囧囧中自有囧囧    時間: 15/4/2010 03:09 AM
某中五會考生路過
今星期先開始溫錯唔好插-︿-
TROLLEY個題
FAN會左吹 推AIR向左 AIR推番TROLLEY向右
向左GE AIR 撞到CARBOARD 推CARBOARD令TROLLEY向左
CARBOARD推番AIR向右
AIR 向左同向右GE力抵消(?!
TROLLEY向左向右GE力相同所以唔旭掛
可能錯-,-
the variation of kinetic energy with time.
a=gsin x
g costant a constant
m constant
k.e vary with t^2
=====================================
wave length of visible violet light in glass is greater than that in air.應該係錯
v =f x (wavelength)
v in glass decrease frequency不變
wavelength decrease 唔太記得係唔係咁解囧rz
=======================================
ce 好似assume左air個係1同vacuum一樣
v of E.M.wave 係光速in air
========================================
話說第二題唔係應該係
T+(mg)=ma
g係negative所以係
T-mg=ma咩
點解係T+mg=ma囧
=========================================
time interval個幾題係take 5個點中間個位計好似係-_,-唔記得囧

---

作者: 小霞的fans    時間: 15/4/2010 03:05 PM


violet visible light係glass既speed慢d定red visible light慢d架!?
書裡面冇提過但係past paper出過!?
同埋呢..
T+(mg)=ma
g係negative所以係
T-mg=ma咩
點解係T+mg=ma囧

點解係+既.....

---

作者: 囧囧中自有囧囧    時間: 15/4/2010 09:33 PM


呀sir話係glass ,red light快過violet
但係wavelength of violet細過red

---

作者: ice    時間: 15/4/2010 11:11 PM

呀sir話係glass ,red light快過violet
但係wavelength of violet大過red唔記得點解lu
囧囧中自有囧囧 發表於 15/4/2010 09:33 PM

                               
登錄/註冊後可看大圖

不是frequency ofviolet>frequency ofred
wavelength ofviolet<wavelength ofred嗎

---

作者: 囧囧中自有囧囧    時間: 15/4/2010 11:42 PM
更正囧我抄錯野--呀sir話係glass ,red light快過violet
wavelength of violet<wavelength of red先岩囧rz
i am so sorry

---

作者: 小霞的fans    時間: 16/4/2010 01:47 PM


30# 囧囧中自有囧囧

potential difference係唔係姐係2點之間voltage既difference呀??

                               
登錄/註冊後可看大圖

我想問X同Y之間既potential difference係幾多??

---

作者: sy    時間: 16/4/2010 02:35 PM

30# 囧囧中自有囧囧  

potential difference係唔係姐係2點之間voltage既difference呀??


我想問X同Y既potential difference係幾多??
小霞的fans 發表於 16/4/2010 01:47 PM

                               
登錄/註冊後可看大圖

potential difference=voltage

---

作者: renz    時間: 18/4/2010 01:21 PM
4. 1997/I/4

                               
登錄/註冊後可看大圖

A student uses the apparatus shown in Figure 5 to perform an experiment to measure the specific latent heat
of fusion of ice. He uses a joulemeter to measure the energy required to melt a certain amount of ice.
(a) Draw a diagram to show how the apparatus can be set up for the experiment. (3 marks)
(b) The following data are obtained in the experiment :
Initial joulemeter reading = 28 000 J
Final joulemeter reading = 40 400 J
Mass of water collected in the beaker = 0.045 kg.
Calculate the specific latent heat of fusion of ice. (3 marks)
(c) Why should the ice used in the experiment be crushed ? (2 marks)
(d) A teacher comments that the result of this' experiment is not accurate. She points out that a control
experiment is required in order to improve the accuracy of the experiment.
*(i) Describe how the control experiment can be set up and explain its function. (5 marks)
(ii) After setting up the control experiment, the student repeats the above experiment. Would you
expect the specific latent heat of fusion obtained to be higher or lower than that obtained in (b)?
Explain your answer. (2 marks)

同埋mc兩題

18. 2000/II/21

                               
登錄/註冊後可看大圖

The above apparatus is used to find the specific latent heat of vaporization of water lv. Which of the following
factors will cause the result obtained to be larger than the true value of lv?
(1) Some energy is lost to the surrounding
(2) Some steam condenses and drips back into the beaker
(3) Some boiling water inside the beaker splashes out of the beaker
A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only E. (1),(2) and (3)


20. 2002/II/21

                               
登錄/註冊後可看大圖

The result obtained in Q.19 is found to be higher than the true value of the specific heat capacity of the
metal. Which of the following is a probable reason?
A. Some hot water is still adhered to the metal block when the block is transferred to cold water.(19)
B. Some energy is lost to the surroundings when the metal block is transferred to cold water.
C. Some energy is absorbed by the cup.
D. The temperature of the metal block is still higher than 38ºC when the final temperature of the water
in the cup is measured.

---

作者: 囧囧中自有囧囧    時間: 18/4/2010 06:06 PM


02 18 同09 第12題一樣-_,-
heat loss to surronding
energy 大左 E=ml
change of mass 不變 l大左
(2) more energy is required to boil to same amount of water
e大左 change of mass不變 l大左
(3) change of mass大左 e不變ge話 l細左
edited
02 20 mm=mass of metal mw
有水係上面 多左一樣野比energy*
之後點自己諗=P

---

作者: pokedigi    時間: 24/4/2010 12:01 PM

30# 囧囧中自有囧囧

potential difference係唔係姐係2點之間voltage既difference呀??

                               
登錄/註冊後可看大圖

我想問X同Y之間既potential difference係幾多??
小霞的fans 發表於 16/4/2010 01:47 PM

                               
登錄/註冊後可看大圖

正確的講voltage只是potential 的單位
so 問p.d.(potential difference)姐是問2點(wire上)的potential差幾多voltage
答案是以V做單位
如果wire 2點之間冇其他野,而resistance of wire=0的話,p.d.就是0(V=IR,R=0)
(ce是比較少出現potential 呢個字,但到al 就會是咁講)
一般而言,一個circuit中,battery的emf
(emf 姐是battery 2邊的p.d.,ce有時都會出現)
是等於任何一條route中所有across其他物件的p.d.的總和
除非條題目有講 internal resistance (battery 自己的 resistance)
不過應該是al 先會問
呢條題目得一條route,一個物件,所以佢的p.d.就=emf=6V

---

歡迎光臨 香港寵物小精靈村落 論壇 (https://proxy.archiver.hkpnve.pokebeacon.com/)

Powered by Discuz! X3.2