lacoste's PHYSICS questions

[lacoste]

Motion
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!

[kurrymuncher]

ms^-2 means that an object is accelerating at x metres per second per second.

If was accelerating at 2m per second per second, that means my speed is increasing by 2m after each second, if that makes sense

[Damo17]

1.) ms^-1 refers to velocity
     ms^-2 refers to acceleration

[lacoste]

why couldn't it just be ms^-1? what does that mean?

i still don't understand it, but thanks kurrymuncher.

[dekoyl]

1) = m/s/s means metres per second per second. You understand velocity right? So 5m/s (velocity) means the object will travel 5 metres every second. Now for acceleration, 5m/s/s or means the object is increasing at a speed of 5m/s every second. So in the first second, he will be traveling at 5m/s. In the second second, he will be traveling at 10m/s and so on.

2)Not understanding the question Sorry

[Damo17]

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.

[lacoste]

rewording the second question.

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.

[lacoste]

what exactly is magnitude?

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?

[kurrymuncher]

For velocity you must state the magnitude and the direction, as vectors require magnitude and a direction. Scalars only require magnitude

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

[lacoste]

How do i determine the direction of the change in velocity?

[lacoste]

i think i have discovered how; its opposite to the path taken.

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!

[Collin Li]

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").

[Collin Li]

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 as well.

The direction should be S51.34E

[lacoste]

thanks.

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

[Collin Li]

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.)