Post by: lacoste on December 08, 2008, 05:13:55 pm
1). I don't get the notation for motion in kinematics of the topic acceleration. Why do we change the unit of ms^-1 to ms^-2?
2). What is the best way to draw the direction of a question...regarding average acceleration... in other words I'm having trouble drawing the 'triangle' that makes up the average acceleration? edit: i dont know where to put the direction of the arrow-head for 'v' and it screws me over when trying to determine the final direction. :crazy2:
any help appreciated!
Post by: kurrymuncher on December 08, 2008, 05:18:35 pm
If was accelerating at 2m per second per second, that means my speed is increasing by 2m after each second, if that makes sense
Post by: Damo17 on December 08, 2008, 05:21:03 pm
ms^-2 refers to acceleration
Post by: lacoste on December 08, 2008, 05:21:50 pm
i still don't understand it, but thanks kurrymuncher.
Post by: dekoyl on December 08, 2008, 05:23:04 pm
2)Not understanding the question :( Sorry
Post by: Damo17 on December 08, 2008, 05:27:53 pm
why couldn't it just be ms^-1? what does that mean?
i still don't understand it, but thanks kurrymuncher.
ms^-1 means how far the object is traveling every second whereas ms^-2 describes how the velocity(ms^-1) changes per second thus obtaining ms^-2.
Post by: lacoste on December 08, 2008, 05:27:59 pm
2). Determine the average acceleration of the following objects.. ..
a). A car travelling due west at a speed of 30ms^-1 turns due north at a speed of 35ms^-1. the change occurs in a time of 2.5s?
i get how to use Pythagoras' theorem but i dont get the final direction which involves drawing the qst out.
Post by: lacoste on December 08, 2008, 05:32:02 pm
is it the size of an object/scalar?
so would it be possible to say this object's velocity has a magnitude of 60 units etc?
Post by: kurrymuncher on December 08, 2008, 05:33:51 pm
Yes it would be possible, but you must also state the direction of the velocity
Yes, you can refer to magnitude as the size of an objects velocity
Post by: lacoste on December 08, 2008, 05:43:29 pm
Post by: lacoste on December 08, 2008, 07:15:28 pm
i think theres a mistake in the handout sheet;in the qst did they leave out the hr^-1 in the 80km section?
Determine the average acceleration of:
a sports car travelling west at 100km/hr^-1 that turns left and slows to a speed of 80km^-1 south. The turn takes 5.0s to complete. Answer in ms^-2?
I got 7.11 ms^-2
and the direction is S53degrees20secondsE? book got different.
thanks for anyhelp!
Post by: Collin Li on December 08, 2008, 07:17:39 pm
How do i determine the direction of the change in velocity?
Final velocity minus initial velocity.
Draw the arrows representing the final velocity, and initial velocity. Reverse the initial velocity arrow, then add that with the final velocity arrow (joining the head of the first arrow with the tail of the next arrow). The overall arrow (from the first arrow's tail to the second arrow's head) is the direction of the "change in velocity").
Post by: Collin Li on December 08, 2008, 07:24:24 pm
i think theres a mistake in the handout sheet;in the qst did they leave out the hr^-1 in the 80km section?
Determine the average acceleration of:
a sports car travelling west at 100km/hr^-1 that turns left and slows to a speed of 80km^-1 south. The turn takes 5.0s to complete. Answer in ms^-2?
I got 7.11 ms^-2
and the direction is S53degrees20secondsE? book got different.
thanks for anyhelp!
Yep, they missed out the "hr" before the "^-1" it seems.
I got
The direction should be S51.34E
Post by: lacoste on December 08, 2008, 07:29:10 pm
how did you get S51.34E?
its driving me nuts!!
the book got the same S51.3E; but when do you drop the four?
i keep on getting a different result! from both coblin and handout sheet/book
Post by: Collin Li on December 08, 2008, 07:45:10 pm
how did you get S51.34E?
its driving me nuts!!
the book got the same S51.3E; but when do you drop the four?
They're probably just stating it to 1 decimal place, rather than 2. It's the same answer (me and the book)
You probably got 53 by using your rounded off values or something like that.
What I did was solve
Post by: lacoste on December 08, 2008, 08:13:47 pm
do i place my final answer as which one of the above?
Post by: Collin Li on December 08, 2008, 08:18:28 pm
direction is S53degrees20secondsE? book got different.
51.34 degrees is equal to 51degrees20seconds.
You wrote 53 in the first post so I thought you did a rounding error or something. Also, it should be 20 minutes, not seconds. :P
Yeah, they're all the same. I think Physics would prefer decimal places (rather than degrees, minutes, seconds)
Post by: lacoste on December 08, 2008, 08:22:07 pm
big thanks for the clear-up!!
Post by: lacoste on December 08, 2008, 09:26:05 pm
how did you get S51.34E?
its driving me nuts!!
the book got the same S51.3E; but when do you drop the four?
They're probably just stating it to 1 decimal place, rather than 2. It's the same answer (me and the book)
You probably got 53 by using your rounded off values or something like that.
What I did was solve(to 2 d.p.)
shouldn't you solve
then, do 90-38.66=51.34 ?
is it possible for a diagram using latex?
100km
----->
\ |
\ |
\ | 80km
V
[then a diagonal line connecting from top left corner to bottom right corner]
use tan. opposite is 80km, adjacent is 100km?
or did you work it out a different way coblin?
Post by: Collin Li on December 08, 2008, 09:42:39 pm
Code: [Select]
upper-right
___
|\ |
| \ |
|__\|
lower-leftThen I used the angle up the top, so that the opposite was 100 and the adjacent was 80, which would directly give me the angle which fits in between S
Post by: lacoste on December 08, 2008, 10:01:14 pm
another question...does significant figures in chemistry and physics differ? if so can you please explain?
Post by: Collin Li on December 08, 2008, 10:14:40 pm
Same meaning. Only difference is that Chemistry cares about it and Physics doesn't really care about it (which is why I arbitrarily chose 2 decimal places).
Post by: lacoste on December 31, 2008, 07:48:07 pm
eg. v=u+at
Is there a method to quickly remember these?
Post by: /0 on December 31, 2008, 07:51:11 pm
Do we have to memorize the Linear Motion formulas? They are given to use on a data booklet but will it be of benefit to memorize ALL or some of those formulas?
eg. v=u+at
Is there a method to quickly remember these?
There are only 5 of them, and they aren't that hard... you should definitely memorize them.
Post by: lacoste on December 31, 2008, 08:19:39 pm
How do I work out the instantaneous speed of a question? without a graph
[is there a quick method?] btw, the book doesn't even have that in an example
Post by: Flaming_Arrow on January 01, 2009, 12:23:32 am
so u = 10 a= 5 t = 7
then just use the equation from there
Post by: lacoste on January 01, 2009, 01:43:28 am
Can somebody shed some light?
Post by: Flaming_Arrow on January 01, 2009, 02:09:32 am
Post by: NE2000 on January 01, 2009, 04:35:59 pm
I have trouble with significant figures in physics. If it doesn't state then what happens?
Can somebody shed some light?
Typically in chemistry you would just go with the lowest number of significant figures present in the question, as it would be inaccurate to present your answers to any higher a level of significant figures. The same generally holds true for physics and any other subject for that matter, only they tend to be more lenient in physics.
So if the question gave you 10.3 m/s, 5.1 m/s/s and 3.45 seconds as your given value, your answer would be to 2 significant figures (like the acceleration value).
Post by: /0 on January 01, 2009, 05:26:07 pm
Post by: lacoste on January 14, 2009, 04:22:33 pm
Do you think it would be safe in physics to 'generally' put your answer to 2 decimal places?
I think 2 or 3 decimal places is the way to go, but not one. But always look at the question in case it asks for more.
Teacher said the the Physics examiners are lenient, and nice. They don't really care about the sig figs unless its too OUTSTANDING. Usually, they look for process work.
Don't rely heavily on the advice from the teacher though because if the exams are 'easy' then the examiners become really tight on sig figs i guess, when they do a massive recheck just like th e06 methods. i highly doubt that would happen to physics though
Post by: lacoste on January 14, 2009, 04:34:45 pm
How do I do the anti-derivative of that to get to this
Q2). When do I use
compared to
Post by: TrueTears on January 14, 2009, 04:52:58 pm
Q1).
How do I do the anti-derivative of that to get to this?
Q2). When do I use
compared to
Q1. so we know
Post by: TrueTears on January 14, 2009, 04:54:57 pm
you use
you use
Post by: lacoste on January 14, 2009, 07:28:37 pm
q). When working out what the instantaneous speed of a question is, which varible is the unknown?
Post by: Flaming_Arrow on January 14, 2009, 07:55:58 pm
thanks true tears. i dont really get antidiff but is not a problem :)
q). When working out what the instantaneous speed of a question is, which varible is the unknown?
v?
Post by: lacoste on January 14, 2009, 08:07:15 pm
thanks true tears. i dont really get antidiff but is not a problem :)
q). When working out what the instantaneous speed of a question is, which varible is the unknown?
v?
Isn't 'v' the final velocity?
what does that mean in context regarding the instantaneous speed and 'v'?
cheers!
Post by: Flaming_Arrow on January 14, 2009, 08:13:50 pm
when they ask you to find instantaneous velocity they normally give you time or distance meaning v will be the final velocity at a particular instant.
Post by: lacoste on January 14, 2009, 08:17:10 pm
v is the final velocity
when they ask you to find instantaneous velocity they normally give you time or distance meaning v will be the final velocity at a particular instant.
Is instantaneous speed the exact same as instantaneous velocity?
Post by: Flaming_Arrow on January 14, 2009, 08:29:47 pm
v is the final velocity
when they ask you to find instantaneous velocity they normally give you time or distance meaning v will be the final velocity at a particular instant.
Is instantaneous speed the exact same as instantaneous velocity?
Post by: lacoste on January 14, 2009, 08:44:33 pm
Post by: Flaming_Arrow on January 14, 2009, 09:22:22 pm
I'm asked to find instantaneous Speed, not instantaneous Velocity ... unless they are related exactly. ?
it depends on the question really.
if your asked to find instantaneous speed and there is a direction given, you don't need to write direction
on the other hand, if its instantaneous velocity you will need to write direction only if its given.
Post by: lacoste on January 14, 2009, 09:26:48 pm
But is instantaneous speed 'v'? and instantaneous velocity also 'v'?
Post by: TrueTears on January 14, 2009, 09:34:19 pm
velocity is denoted by
if u want to be technical
Post by: lacoste on January 14, 2009, 09:39:37 pm
speed is denoted by.
velocity is denoted by.
if u want to be technical
nope not technical, i just thought that there was another variable for instantaneous velocity
thanks flaming arrow and true tears !!