Shannon.Leanne
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I need help with this question please, thank you!

3. A car travels with uniform acceleration between three lamp posts, equally spaced at 18 m apart. It passes the second post 2 seconds after passing the first post and passes the third post 1 second later.
(a) Find the car’s acceleration
(b) Find the car’s velocity when it passes the first post
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RogerOxon
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(Original post by Shannon.Leanne)
I need help with this question please, thank you!

3. A car travels with uniform acceleration between three lamp posts, equally spaced at 18 m apart. It passes the second post 2 seconds after passing the first post and passes the third post 1 second later.
(a) Find the car’s acceleration
(b) Find the car’s velocity when it passes the first post
You have speeds of u, u + 2a and u + 3a. Write equations for the distance traveled (average speed times time) between the posts and solve.

What is the average speed between the first and second posts?
And between the second and third posts?

Please post your working if you have any issues.
Last edited by RogerOxon; 1 year ago
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Shannon.Leanne
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(Original post by RogerOxon)
You have speeds of u, u + 2a and u + 3a. Write equations for the distance traveled (average speed times time) between the posts and solve.

What is the average speed between the first and second posts?
And between the second and third posts?

Please post your working if you have any issues.
Thank you so much, I got the right answer for a, however I can’t seem to do b. I got that t=2, but when I put it into v=u+at I don’t get the right answer
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RogerOxon
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(Original post by Shannon.Leanne)
Thank you so much, I got the right answer for a, however I can’t seem to do b. I got that t=2, but when I put it into v=u+at I don’t get the right answer
The first post is at t=0, i.e. u.
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Shannon.Leanne
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(Original post by RogerOxon)
The first post is at t=0, i.e. u.
So s=18, A=6 and t=0, correct? I can’t seem to figure out which sugar equation to put it into
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RogerOxon
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(Original post by Shannon.Leanne)
So s=18, A=6 and t=0, correct? I can’t seem to figure out which sugar equation to put it into
How did you get a=6 (correct)? One of the equations used to calculate it will now get you u.
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Shannon.Leanne
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(Original post by RogerOxon)
How did you get a=6 (correct)? One of the equations used to calculate it will now get you u.
I just assumed because in the question it says “with uniform acceleration”?
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RogerOxon
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(Original post by Shannon.Leanne)
I just assumed because in the question it says “with uniform acceleration”?
We use distance = average speed * time.

For the first pole interval:

s = \frac{u + u + 2a}{2} 2 = 2u + 2a

\therefore 2u + 2a = 18

Do the same for the second pole interval, where the speed goes from u + 2a to u + 3a.

You then have two equations in u and a, so can solve for both.
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Shannon.Leanne
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(Original post by RogerOxon)
We use distance = average speed * time.

For the first pole interval:

s = \frac{u + u + 2a}{2} 2 = 2u + 2a

\therefore 2u + 2a = 18

Do the same for the second pole interval, where the speed goes from u + 2a to u + 3a.

You then have two equations in u and a, so can solve for both.
I’ve figured it out now, thank you so much for your help!
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zoe2002
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i hate statistics anyone else doing it too
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