# Physics A level dynamics question

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#1
I am confused about the mark scheme answer for part d(ii) in the following question:

This is the mark scheme answer:

Instead of using v = at as the mark scheme does, I used v = sqrt(2*a*s), where s = 1.0m and a = 9.8/s. But my method gives 4.4m/s and the mark scheme says 4.1m/s. Why is my method incorrect here?
Last edited by Orlqndo; 2 weeks ago
0
2 weeks ago
#2
(Original post by Orlqndo)
I am confused about the mark scheme answer for this following question:

This is the mark scheme answer:

Instead of using v = at as the mark scheme does, I used v = sqrt(2*a*s), where s = 1.0m and a = 9.8/s. But my method gives 4.4m/s and the mark scheme says 4.1m/s. Why is my method incorrect here?
Maybe this is me being stupid, but the mark scheme you've screenshotted shows the answer to Part 2, but the question is for Part 3
3
2 weeks ago
#3
(Original post by Kerchoo95)
Maybe this is me being stupid, but the mark scheme you've screenshotted shows the answer to Part 2, but the question is for Part 3
Yup, part 1 and 2 are missing which may be needed to answer the OP's question.
0
#4
(Original post by 0le)
Yup, part 1 and 2 are missing which may be needed to answer the OP's question.
Sorry my bad - I've edited the original post so it has the entire question. My question is about part d(ii).
2
2 weeks ago
#5
(Original post by Orlqndo)
Sorry my bad - I've edited the original post so it has the entire question. My question is about part d(ii).

Part d states 'after leaving the ramp at B the skateboarder lands at C 0.42 seconds later.

The question wants you to use the time value stated and hence the appropriate suvat is v = u + at
1
2 weeks ago
#6
(Original post by Orlqndo)
Sorry my bad - I've edited the original post so it has the entire question. My question is about part d(ii).
The information given in the question is not consistent with suvat.

To descend 1m with zero initial velocity would take 0.452s (3sig.fig.) using g=9.8m/s/s - not 0.42s. And that's why you get a different answer if you use

As uberteknik said, they're expecting you to use

There's nothing wrong with your working, IMO - it's just a very poorly constructed question.
Last edited by ghostwalker; 2 weeks ago
1
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