The Student Room Group

M2 projectiles

Are you allowed to quote the formula for the equation of the trajectory in the exam or do you have to derive it every time?
y=xtanθx2gsec2θ2u2 y=x\tan \theta-\frac{x^2g\sec^2 \theta}{2u^2}
The old textbook I have quotes it for most problems but the Edexcel textbooks barely use it.
Original post by solC
Are you allowed to quote the formula for the equation of the trajectory in the exam or do you have to derive it every time?
y=xtanθx2gsec2θ2u2 y=x\tan \theta-\frac{x^2g\sec^2 \theta}{2u^2}
The old textbook I have quotes it for most problems but the Edexcel textbooks barely use it.


You'd have to derive it if it's not in the formula booklet.
Reply 2
Original post by RDKGames
You'd have to derive it if it's not in the formula booklet.


Oh okay thanks
Reply 3
Original post by solC
Oh okay thanks


It takes about 2 lines to derive anyway,
Reply 4
Original post by solC
Oh okay thanks


There are exam questions where you have to derive the formula, but it's straightforward as Zacken said. You might as well learn the derivation.
Original post by RDKGames
You'd have to derive it if it's not in the formula booklet.


If that were the case, then presumably you would also have to derive
v^2 = u^2 + 2as
every time you used it.
Original post by solC
Are you allowed to quote the formula for the equation of the trajectory in the exam or do you have to derive it every time?
y=xtanθx2gsec2θ2u2 y=x\tan \theta-\frac{x^2g\sec^2 \theta}{2u^2}
The old textbook I have quotes it for most problems but the Edexcel textbooks barely use it.


If Edexcel questions need it, they generally ask you to derive it.

Otherwise, you can quote it, but if so, please make sure that you've got it correct. An incorrect formula would mean that you'd lose all of the marks.
Original post by tiny hobbit
If that were the case, then presumably you would also have to derive
v^2 = u^2 + 2as
every time you used it.


It is that case.

You're expected to remember SUVAT equations and you're free to use them as they're on the spec, and they're the basis of Mechanics 2. That is not the case with the projectile one.
Original post by RDKGames
It is that case.

You're expected to remember SUVAT equations and you're free to use them as they're on the spec, and they're the basis of Mechanics 2. That is not the case with the projectile one.


We must agree to have different opinions on this.
Reply 9
I haven't seen it used in the new edexcel textbook, how does the formula help with projectiles questions?
Reply 10
What an absurdly specific formula to memorise. I despair.
Reply 11
Original post by metrize
I haven't seen it used in the new edexcel textbook, how does the formula help with projectiles questions?


Just saves a few lines, but i'm a lazy bugger so...
Original post by metrize
I haven't seen it used in the new edexcel textbook, how does the formula help with projectiles questions?


Original post by mik1a
What an absurdly specific formula to memorise. I despair.


It is occasionally useful, particularly if the angle of projection is unknown. If it is needed, Edexcel will generally ask you to derive it,as in June 2011. To do this you use s = ut horizontally and s = ut + 0.5at^2 vertically and then eliminate t.

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