Help with Edexcel M1 (Review Exercise 1)

Hello, so my teacher assigned me to do the first 30 questions of the review exercise and funnily enough Q30 is the one question I just don't understand. I've looked at physicsandmathstutor.com and I still don't understand. The discs don't work on W10 and my friend who did them before the end of term on Friday asked the teacher but still doesn't fully understand the question.

Thanks.

Gave my text book back earlier in the month, how I miss school but if you want to upload a picture or send me a link to find the question/solution, I can give you a hand (struggling to find it online atm)

Thanks

https://534ff63a01f6cb44c9c4e69801769b0628cd58d1.googledrive.com/host/0B1ZiqBksUHNYdG9SOEVLaTVSYUE/REV1.pdf

Q30

Just cooking myself tea, I'll get back to you in a bit ;D

Take as much time as you like, I've been working all day so I'm relaxing now so dw about doing your dinner fast. Plz plz plz don't prioritize me.

Right, so I assume you're pretty clever if you've done the previous 29, do you get how they've done the graph, with regards to f and then t?

Hello, so my teacher assigned me to do the first 30 questions of the review exercise and funnily enough Q30 is the one question I just don't understand. I've looked at physicsandmathstutor.com and I still don't understand. The discs don't work on W10 and my friend who did them before the end of term on Friday asked the teacher but still doesn't fully understand the question.

Thanks.

So what have you got so far? Ignore the solution and post what you've done.

108Kmh^-1 = 30ms^-1
36Kmh^-1 = 10ms^-1
4Km = 4000m

Drawn foundation of graph as well.

Yeah, I know, not that good

That's a start!

Can you find some times for decel and accel as a function of f?

Ditto distance travelled for each of the three stages?

Uhhh no. Help plz.

You've met suvat?
first part of journey:
v = 30
u = 10
a = - 3f
t

etc

We've got to use the total distances and times we've been given somehow.

Ah SUVat didn't think of that! There's me always over complicating things!
So since accel is the gradient (I haven't learnt diff in C1 yet so I'll call it gradient)
the accel 3f is equal to 20/t? That makes the second trapezium accel f = 20/3t?
Am I right?

Firstly note my correction - I got u and v round the wrong way - trying to mark and help you at the same time!

Hahahaha it's ok mistakes are mistakes

What next?

Use suvat to get times for accel and decel in terms of f.

Have you done that?

Then we know 240 = accel time + decel + constant vel time

We can rearrange to get constant vel time in terms of f.

Yeah so 3f = 20/t and therefore f = 20/3t.

T = 3t so accel = 20/3T
I'm not sure now

I got

first time for accel = 20/(3f)
time for decel = 20/f

you don't want more variables!!

So can you find time at constant speed?

If you have distance. Or use SUVat? Or lookie lookie at de shape?

So for the central bit 240 - 4t...why?

*dalek voice* Explain plz