IB HL Physics discussions

[Mr Taylor]

Many times students email me with questions and the answers I give
would be good for all to see, since I'm sure you may have had a
similar problem. Instead of emailing me we could post the problems
here and invite others (including me!) to help out. That way we all
get a share of the learning...win win?

[Mr Taylor]

For example, here is an email from Ben asking about a recent
projectile motion:


-----Original Message-----
From: Benjamin (Ben) Heuze
Sent: Friday, May 07, 2010 9:08 PM
To: Brian Taylor
Subject:

Dear Mr. Taylor,

For Question 1 of the IB questions of projectile motion, i do not
understand why do we have to find the magnitude of the velocity of
horizontal and vertical when we have also found the velocity v using
v2=u2 + 2as.

Regards,

Ben heuze 12L

[Mr Taylor]

And here is the reply:

-----Original Message-----
From: Brian Taylor
Sent: Saturday, May 08, 2010 11:44 AM
To: Benjamin (Ben) Heuze
Subject: RE:

Hi Ben

This is because the speed is has both a vertical and horizontal
component. You have only found the vertical velocity v using v2=u2 +
2as. You need to use this along with the horizontal velocity and
Pythagoras to find the speed it hits the water. The language in this
question is interesting because if it asked for the velocity then you
would have to give the angle also (since velocity is a vector), but it
simply asks for the speed.

Mr Taylor

[Mr Taylor]

and here is another great question from Ben with my answer!

Hi Ben

The mathematics of working out the work done is a little tricky,
basically you have to find the area under the curve by integrating the
F = -Gmm/r2 equation. Work done = force x distance, which is the area
under the line (just like the potential energy in a spring is the area
under the force vs extension curve). We will discuss in class next
week. I am happy to see you have read ahead and discovered a tricky
part of the syllabus - welcome to HL!

Mr Taylor

-----Original Message-----
From: Benjamin (Ben) Heuze
Sent: Friday, May 07, 2010 10:36 PM
To: Brian Taylor
Subject:

Dear Mr. Taylor,

Sorry to disturb you again but from reading the assigned pages, i dont
really understand the topic of working out work done from the graph of
F = -Gmm/r2 and also in the topic of earth satellites in the book it
said that in a high satellite ( big r). does it mean that in a high
satellite there is a large r compared to a low orbit satellite?

Regards,

Ben Heuze 12L