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Mech resistance q

Need help.on part 2b. How can you get a 'value'? Barely anything cancels.

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Original post by cooldudeman
Need help.on part 2b. How can you get a 'value'? Barely anything cancels.

Posted from TSR Mobile


Write acceleration as v.dv/dx and solve differential equation.
Reply 2
Original post by brianeverit
Write acceleration as v.dv/dx and solve differential equation.


Why is it a=v.dv/dt and not a=dv/dt?
Im guessing v=s.ds/dt as well
I even checked on this website.

Im assuming that the picture only applies when you have everything in terms of t right?

No one told me this stuff
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(edited 10 years ago)
Original post by cooldudeman
Why is it a=v.dv/dt and not a=dv/dt?


Read brianeverit's post again, he didn't say "v.dv/dt".

His suggestion is a standard technique introduced at A-level.

Comes from

a=dvdt=dvdx×dxdt=vdvdx\displaystyle a=\frac{dv}{dt}= \frac{dv}{dx}\times\frac{dx}{dt}= v\frac{dv}{dx}
Reply 4
Original post by ghostwalker
Read brianeverit's post again, he didn't say "v.dv/dt".

His suggestion is a standard technique introduced at A-level.

Comes from

a=dvdt=dvdx×dxdt=vdvdx\displaystyle a=\frac{dv}{dt}= \frac{dv}{dx}\times\frac{dx}{dt}= v\frac{dv}{dx}


Ohhhh okok thats not confusing anymore then.

So does that mean that I didn't do the first part completely wrong

Posted from TSR Mobile
Original post by cooldudeman

So does that mean that I didn't do the first part completely wrong


First part for time at max height was fine.
Original post by cooldudeman
Why is it a=v.dv/dt and not a=dv/dt?
Im guessing v=s.ds/dt as well
I even checked on this website.

Im assuming that the picture only applies when you have everything in terms of t right?

No one told me this stuff
Posted from TSR Mobile


acceleration = dv/dt or v.dv/dx. I didn't say anything about v.dv/dt
Reply 7
Original post by brianeverit
acceleration = dv/dt or v.dv/dx. I didn't say anything about v.dv/dt


Original post by ghostwalker
First part for time at max height was fine.


I did what you said but still didnt get an actual value.

Posted from TSR Mobile
Original post by cooldudeman
I did what you said but still didnt get an actual value.

Posted from TSR Mobile


By "actual value" , do you mean you are trying to get a single numerical value? I don't see how that would be possible. The height is bound to be some function of U and k. btw the second term in your first integration should be + not -
Reply 9
Original post by brianeverit
By "actual value" , do you mean you are trying to get a single numerical value? I don't see how that would be possible. The height is bound to be some function of U and k. btw the second term in your first integration should be + not -


Oh so the answer can be in terms of k and U. Ive never come across a question that said 'value' when it didn't mean a numerical one.

Yeah ill fix it

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