# Mechanics help (SUVAT)

How would you go about doing this question. What approach is required

So you have points xyz. XY=YZ=2km
It takes 100s to go from x to z. And 150s from Y to Z. What is the magnitude of deceleration assuming it is constant. And how far does the car travel beyond Z
(edited 1 year ago)
Original post by abcd678
How would you go about doing this question. What approach is required

So you have points xyz. XY=YZ=2km
It takes 100s to go from x to z. And 150s from Y to Z. What is the magnitude of deceleration assuming it is constant. And how far does the car travel beyond Z

Presume its 100s to go from x to y, otherwise it doesnt make sense. Youve got two simultaneous equations involving s, t, a and another variable (u say). So formulate them and solve.
Original post by mqb2766
Presume its 100s to go from x to y, otherwise it doesnt make sense. Youve got two simultaneous equations involving s, t, a and another variable (u say). So formulate them and solve.

How would I essentially right them both out. If you could please illustrate
(edited 1 year ago)
Original post by abcd678
How would I essentially right them both out. If you could please illustrate

There is only one suvat equation which involves the 4 variables mentioned, so you could use that one (twice) for two segments. A bit of thinking about which segments to use simplifies the problem. So have a think and post your thoughts/progress.
Original post by mqb2766
There is only one suvat equation which involves the 4 variables mentioned, so you could use that one (twice) for two segments. A bit of thinking about which segments to use simplifies the problem. So have a think and post your thoughts/progress.

I'm thinking of s=1/2(u+v)t
And then applying v^2=u^2+2as for a
But the thing is as I don't know two variables a and s. I am struggling to solve
If I can find one more variable e.g. either a or s. I will be able to solve but how?
(edited 1 year ago)
Original post by abcd678
I'm thinking of s=1/2(u+v)t
And then applying v^2=u^2+2as for a
But the thing is as I don't know two variables a and s. I am struggling to solve

It would probably help to draw a diagram for the two sections of motion, marking on it what you know / have to find. You know s and t for each section and want to find a which is the same on both sections. As you have two sections/equations you could also try and find the initial velocity u at the same time as a and solve them simultaneously.

(edited 1 year ago)
Original post by mqb2766
It would probably help to draw a diagram for the two sections of motion, marking on it what you know / have to find. You know s and t for each section and want to find a which is the same on both sections. As you have two sections/equations you could also try and find the initial velocity u at the same time as a and solve them simultaneously.

I'm using a=2S/t^2
Ok so from x to y the acceleration is given by 2*2000/100^2
And for y to z the acceleration is given by 2*2000/150^2

What do I do now?
(edited 1 year ago)
Original post by abcd678
I'm using a=2S/t^2
Ok so from x to y the acceleration is given by 2*2000/100^2
And for y to z the acceleration is given by 2*2000/150^2

What do I do now?

Did you not sketch the info as suggested and upload?

For the bold, it that would assume the initial velocity is zero which isnt stated and is incorrect. The car is decelerating as it passes through x, y and z so it must have a non-zero velocity at those points.

As in the previous posts, you need to write two simultaneous equations involving a and u (say) and then solve for them.
Original post by mqb2766
Did you not sketch the info as suggested and upload?

For the bold, it that would assume the initial velocity is zero which isnt stated and is incorrect. The car is decelerating as it passes through x, y and z so it must have a non-zero velocity at those points.

As in the previous posts, you need to write two simultaneous equations involving a and u (say) and then solve for them.

I don't understand what you are trying to say. That's reason I posted on this website to get help but you are just confusing me even more. Please can you write out the simultaneous equations and draw me a diagram so I can understand the question. If I could write out the simultaneous equations I wouldn't even asked for help in the first place. My knowledge of mechanics is not good as I've just started the course. So please could you write out the simultaneous equations so I can input the data and solve it.
Original post by abcd678
I don't understand what you are trying to say. That's reason I posted on this website to get help but you are just confusing me even more. Please can you write out the simultaneous equations and draw me a diagram so I can understand the question. If I could write out the simultaneous equations I wouldn't even asked for help in the first place. My knowledge of mechanics is not good as I've just started the course. So please could you write out the simultaneous equations so I can input the data and solve it.

If youre having trouble getting started there is a reasonable overview in
https://www.savemyexams.co.uk/as/maths_mechanics/edexcel/18/revision-notes/2-kinematics/2-3-constant-acceleration---1d/2-3-2-suvat-in-1d/
but just google for others. For a sketch, you don't need to draw a bike/car but mark the points

x ------------------------ y --------------------------- z

and put on distances, times, velocities, acceleration at the appropriate points. Youre given the distances xy and yz and the times it takes for those segments so mark those on. The deceleration is constant throughout. So the other suvat information (unknown) is the velocity at each of the points which represents the initial/final velocity for each suvat phase xy and yz or even xz. So think how you can form two suvat equations for two of those three segments and solve for one of the velocities at the same time as the deceleration.
Original post by mqb2766
If youre having trouble getting started there is a reasonable overview in
https://www.savemyexams.co.uk/as/maths_mechanics/edexcel/18/revision-notes/2-kinematics/2-3-constant-acceleration---1d/2-3-2-suvat-in-1d/
but just google for others. For a sketch, you don't need to draw a bike/car but mark the points

x ------------------------ y --------------------------- z

and put on distances, times, velocities, acceleration at the appropriate points. Youre given the distances xy and yz and the times it takes for those segments so mark those on. The deceleration is constant throughout. So the other suvat information (unknown) is the velocity at each of the points which represents the initial/final velocity for each suvat phase xy and yz or even xz. So think how you can form two suvat equations for two of those three segments and solve for one of the velocities at the same time as the deceleration.

I've managed to calculate the acceleration but how do I calculate the distance travelled beyond z
Original post by abcd678
I've managed to calculate the acceleration but how do I calculate the distance travelled beyond z

Can you upload what youve done?

The extra suvat section (z ...) should be on the diagram and marking on the velocity at the end may help.
(edited 1 year ago)