Projectile Motion (1 Viewer)

[DigitalFortress]

This is fk'd,
I'm good at all of space EXCEPT for this section. So annoying.
Do you ppl have an order in which u can solve these problems?
i.e an order in which to use which equations??

 

[rama_v]

Use 3 unit, its much simpler and easier to understand

Otherwise write down all teh given information, and calculate the horizontal and vertical velocities at the very least. Then try to find the time of flight, hence from there u can work out the maximum height and the range.

 

[Captain Gh3y]

Often, but not always, the first step is to use v = u +at to find the time, by letting v = 0 at the max height (stationary point) of the motion, and solving to find the time for half the flight, then using t to calculate whatever else the quesiton asks for.

 

[Jago]

look at what you have, then look at the formula sheet and 90% of the time you can tell which formula you need.

or, you can use 3u like rama said.

:/ because of 3u everytime i see max height i think make y' = 0

 

[richz]

as rama and jago said, write down all the info ur given then look at the eqns and u shud work it out

 

[serge]

i.e an order in which to use which equations??

It'll all depend on the type of question they
give, theres no point using formulas in
order if they dont lead you anywhere?

 

[Riviet]

If you wanna overcome this fairly big chunk of the space topic, get a whole lot of PM questions and do just 1 each night for a month and i promise you will never have to spend time studying for it when the exams approach.

 

[Abtari]

elegant explanation?

slightly off topic, but didnt wanna create a new thread for this so..

for space, i know this is so lame, but could someone explain how u would:

'explain that a change in gravitational PE is related to work done'

i mean i can do it...but not very elegantly or 'nicely' if u know wot i mean... i dont wont the examiner to have to look at it and go 'huh?' so yeah... and im not sure if im explaining it rightly or adequately myself...

some maths in it to explain the situation would make it even more elegant..

 

[helper]

Look http://community.boredofstudies.org/showthread.php?t=90419

 

[KFunk]

slightly off topic, but didnt wanna create a new thread for this so..

for space, i know this is so lame, but could someone explain how u would:

'explain that a change in gravitational PE is related to work done'

i mean i can do it...but not very elegantly or 'nicely' if u know wot i mean... i dont wont the examiner to have to look at it and go 'huh?' so yeah... and im not sure if im explaining it rightly or adequately myself...

some maths in it to explain the situation would make it even more elegant..

Take an example of the Earth and a satellite. You have to do work in order to move the satellite to a distance further away (against the force of gravity). In doing this the satellite gains potential energy.

The satellite does work itself if it approaches the earth. In this case the satellite looses potential energy and does work via the force of gravity.

If you want the maths: the amount of work done can be evaluated as an integral (using S to represent the integral sign) where the integral is:

S F(x) dx (from x₁ to x₂).... where F(x) is a function describing force. This will give you the work done between x₁ and x₂.

You can do the same thing for gravitational force GMm/r² between the two points r₁ and r₂:

S GMm/r² dr = [ -GMm/r ] between r₁ and r₂

= GMm/r₂ - GMm/r₁

You can probably see that this pretty much the same thing as the difference in gravitational potential energy at the points.

 

[Abtari]

yup so diff in gravitational pe = work done coolies thanks heaps kfunk