Mastering Mechanics SUVAT

I know it may seem easy to some of you.
I’ve done AQA a level maths exams and I found them easy.
It didn’t come up.

I’m using the CIE textbook and the questions are really difficult. How can I master these questions?

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Reply 1

KallamSamad

@mqb2766 @DFranklin @Muttley79

Reply 2

mqb2766

Original post by KallamSamad

I know it may seem easy to some of you.
I’ve done AQA a level maths exams and I found them easy.
It didn’t come up.
I’m using the CIE textbook and the questions are really difficult. How can I master these questions?

There are generally only a smallish number of difficult suvat questions, so the usual is to post ones youre stuck with and any ideas and ask for a hint.

But the usual stuff for understanding suvat is for a question

•

sketch the problem, marking on important info (suvat variables), making clear which is the +ive direction

•

writing down the relevant suvat equations and the variables you know and which one(s) you need to find

•

the actual equations are linear/quadratic, so their solution shouldnt be relatively straightforward.

Similarly, it may help to be able to derive the various suvats from each other (and using calculus) and their relationship with momentum and energy.

Reply 3

KallamSamad

Original post by mqb2766

There are generally only a smallish number of difficult suvat questions, so the usual is to post ones youre stuck with and any ideas and ask for a hint.
But the usual stuff for understanding suvat is for a question

•

sketch the problem, marking on important info (suvat variables), making clear which is the +ive direction

•

writing down the relevant suvat equations and the variables you know and which one(s) you need to find

•

the actual equations are linear/quadratic, so their solution shouldnt be relatively straightforward.

Similarly, it may help to be able to derive the various suvats from each other (and using calculus) and their relationship with momentum and energy.

I’ll post some questions as I go on and I’m planning on restarting the review excercise.

By drawing a diagram would drawing a graph help?
Also is it normal in cie to have weird answers ? Such as irrational numbers? Because in AQA I’d get whole number solutions which made me confident with the answer?

I’m branching off into something deep by asking how would I develop a problem solving mindset?

Reply 4

mqb2766

Original post by KallamSamad

I’ll post some questions as I go on and I’m planning on restarting the review excercise.
By drawing a diagram would drawing a graph help?
Also is it normal in cie to have weird answers ? Such as irrational numbers? Because in AQA I’d get whole number solutions which made me confident with the answer?
I’m branching off into something deep by asking how would I develop a problem solving mindset?

Depending on the question, a sketch of the scenario (ball/cliff/car...) and/or the graph of the relevant suvat variables generally helps and as youre often solving quadratics, you can get surd solutions.

For suvat problems, there isnt necessarily a great deal of problem solving, though drawing a sketch (scenario and/or graph) and getting in the habit of guestimating answers and/or verifying solutions is good.

Reply 5

KallamSamad

Original post by mqb2766

Depending on the question, a sketch of the scenario (ball/cliff/car...) and/or the graph of the relevant suvat variables generally helps and as youre often solving quadratics, you can get surd solutions.
For suvat problems, there isnt necessarily a great deal of problem solving, though drawing a sketch (scenario and/or graph) and getting in the habit of guestimating answers and/or verifying solutions is good.

Is there any short cut scenarios ?
I’ve noticed a lot of the questions when it says “acceleration then goes at a constant speed” you use s=vt.

Have you got any shortcuts like that?

Reply 6

mqb2766

Original post by KallamSamad

Is there any short cut scenarios ?
I’ve noticed a lot of the questions when it says “acceleration then goes at a constant speed” you use s=vt.
Have you got any shortcuts like that?

wbf, you really need to think about/sketch the problem (varaibles) so for your example youre assuming that acceleration is zero so its the usual speed-distance-time (velocity-displacement-time) which you learnt about a long time ago. Zero acceleration suvat is a special case, but most questions have a non-zero acceleration.

Reply 7

KallamSamad

Original post by mqb2766

What does wbf mean?

Reply 8

mqb2766

Original post by KallamSamad

What does wbf mean?

Without being funny. Youre dealing with linear and/or quadratics (suvat variables), so reasoning about them shouldnt be hard if youre systematic.

Reply 9

KallamSamad

Original post by mqb2766

Without being funny. Youre dealing with linear and/or quadratics (suvat variables), so reasoning about them shouldnt be hard if youre systematic.

Ok I’ll try some and post the ones and struggling. Thanks!

Reply 10

KallamSamad

Original post by mqb2766

Without being funny. Youre dealing with linear and/or quadratics (suvat variables), so reasoning about them shouldnt be hard if youre systematic.

I finally get what you mean.
I was doing the problems by doing it in the GCSE way. By listing all the variables without looking at what the question wants and know I’ve sort of got it

Reply 11

KallamSamad

Original post by KallamSamad

I finally get what you mean.
I was doing the problems by doing it in the GCSE way. By listing all the variables without looking at what the question wants and know I’ve sort of got it

Obviously I’ll work on keeping my working tidier

Reply 12

KallamSamad

Original post by mqb2766

Without being funny. Youre dealing with linear and/or quadratics (suvat variables), so reasoning about them shouldnt be hard if youre systematic.

Any tips on how to approach 9b? I’ve got 9a correct but I don’t seem to be able to form this quadratic. When using inequalities what should I do ? Use discriminant?

Reply 13

mqb2766

Original post by KallamSamad

Any tips on how to approach 9b? I’ve got 9a correct but I don’t seem to be able to form this quadratic. When using inequalities what should I do ? Use discriminant?

Ive not worked it though, but both the lion and zebra are in a suvat phase for t>8s and you know their displacements and velocities at that time, so get the difference in displacements which is a quadratic in t, then use the usual discriminant/complete the square to analyse it.

Edit - the "hence" in part b) means analyse the quadratic directly, though the point of closest approach (if it doesnt catch it) can be easily justified by thinking about the time when the velocities are equal, so theyre both moving at the same velocity.