Using Energy isntead of motion formulas. (1 Viewer)

[Xayma]

Are you allowed to use energy formulas instead of motion formulas for physics as in more complex/long questions energy formulas can be quicker.

I know in the VCE a few years ago there was a question were using energy took 2 steps but using motion formulas uses 9 steps.

I know when you have to find time etc it can take longer but generally it doesnt.

For Example.

Find the maximum height a cannonball will reach when launched from a cannon at an angle of 60degrees to the horizontal with a speed of 100ms^-1 Using g as 10.

Using motion formulas you have to find values for time and round off or work with surds but using energy you get:

Let E_g be energy on ground.
Let E_f be energy at max height.

E_g=E_f
1/2mv_g²+mgh_g=1/2mv_f²+mgh_f
m(1/2v_g²+gh_g)=m(1/2v_f²+gh_f)
1/2x100²+10x0=1/2x50² (50 being 100cos 60) + 10xh_f
3750/10=h_f
h_f=375m

 

[abdooooo!!!]

here is what i think.... NO.

those pendatic no math teacher will destroy you for sure even if the answer is the same.

edit: hey what the hell is VCE? is that victorian system of hsc? how would you know they have certain things LOL.

 

[t-i-m-m-y]

wouldn't recommend energy

BOS uses motion formulas just stick with them

 

[Xayma]

Originally posted by abdooooo!!!
edit: hey what the hell is VCE? is that victorian system of hsc? how would you know they have certain things LOL.

Cause we get the Hearld Sun on the border

Originally posted by t-i-m-m-y
wouldn't recommend energy

Bah, but energy is so much easier. Thats my Engineering Studies teacher told us would be easier for alot of questions.

 

[wogboy]

It's OK to use energy formulas rather than the laws of Newtonian motion as long as you use them correctly and get the same answer, I've heard of a few people doing it in the HSC exams.

For kinematics (which is basically all you study in the HSC, just motion), there's not really any benefit of using energy formulas though, might as well stick to the standard Newton equations which you're taught.

For dynamics though (which is stuff where alot of forces are involved, like you did back in prelim), then it is often easier to use energy formulas rather than Newton's equations of motion.

e.g. If you had to answer a question where a mass is pushed with a constant force into a wall, and you're asked what's the kinetic energy of the collision, then it's better to equate the work done on the mass (F*d) with the final kinetic energy, rather than going to the unnecessary trouble of working out the acceleration, then final velocity, then kinetic energy etc.

 

[t-i-m-m-y]

Originally posted by wogboy
It's OK to use energy formulas rather than the laws of Newtonian motion as long as you use them correctly and get the same answer, I've heard of a few people doing it in the HSC exams.

For kinematics (which is basically all you study in the HSC, just motion), there's not really any benefit of using energy formulas though, might as well stick to the standard Newton equations which you're taught.

For dynamics though (which is stuff where alot of forces are involved, like you did back in prelim), then it is often easier to use energy formulas rather than Newton's equations of motion.

e.g. If you had to answer a question where a mass is pushed with a constant force into a wall, and you're asked what's the kinetic energy of the collision, then it's better to equate the work done on the mass (F*d) with the final kinetic energy, rather than going to the unnecessary trouble of working out the acceleration, then final velocity, then kinetic energy etc.

yeah very true
HSC don't need the energy stuff

 

[abdooooo!!!]

hsc don't need math... most of the time

 

[Xayma]

Originally posted by abdooooo!!!
hsc don't need math... most of the time

I know, I just like using energy formulas as it doesnt require as much rounding (first the y-component then time then this etc.)