# A2 Mechanics question

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Can anyone help with this question (I’ve added a picture below, it’s N2) , the answer is 15.3 degrees

Last edited by emma64; 8 months ago

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#3

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**emma64**)If you know the position, differentiate to get the velocity (direction of motion).

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#4

You need to find the arctan of both the position vector and the velocity vector and find the difference between them.

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#5

(Original post by

Can anyone help with this question (I’ve added a picture below, it’s N2) , the answer is 15.3 degrees

**emma64**)Can anyone help with this question (I’ve added a picture below, it’s N2) , the answer is 15.3 degrees

**r**. Now differentiate wrt t to get a formula for

**v**, into which you also plug t=2. The angle you want is now obtained by using the standard dot product formula cos(θ) =

**r**∙

**v**/|

**r**||

**v**|

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#6

(Original post by

Plug t=2 into the original formula to get the position vector

**David Getling**)Plug t=2 into the original formula to get the position vector

**r**. Now differentiate wrt t to get a formula for**v**, into which you also plug t=2. The angle you want is now obtained by using the standard dot product formula cos(θ) =**r**∙**v**/|**r**||**v**|
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#7

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The dot product is not part of the A Level spec anymore.

**Sir Cumference**)The dot product is not part of the A Level spec anymore.

**Bloody hell!!!**That's some real serious dumbing down. I hope most teachers have the good sense to teach it anyway. It's so important that the exam boards ought to be truly ashamed of removing this. So much for making exams more rigorous, especially when I think of some of the stuff they have introduced that is

**far less useful**.

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#8

(Original post by

**David Getling**)**Bloody hell!!!**That's some real serious dumbing down. I hope most teachers have the good sense to teach it anyway. It's so important that the exam boards ought to be truly ashamed of removing this. So much for making exams more rigorous, especially when I think of some of the stuff they have introduced that is**far less useful**.I agree that moving most of C4 vectors to FM was a bit of a strange decision but aside from that I think the increase in difficulty and focus on proof & modelling have been positive overall. They probably had to make a decision to get rid of one of the major topics and it was vectors that got the chop.

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#9

(Original post by

Teachers should be focusing on topics that are on the spec in my opinion. There are lots of very important topics in further maths but they can't all be taught to A Level maths students. The exams have been designed so that the dot product formula is not necessary.

I agree that moving most of C4 vectors to FM was a bit of a strange decision but aside from that I think the increase in difficulty and focus on proof & modelling have been positive overall. They probably had to make a decision to get rid of one of the major topics and it was vectors that got the chop.

**Sir Cumference**)Teachers should be focusing on topics that are on the spec in my opinion. There are lots of very important topics in further maths but they can't all be taught to A Level maths students. The exams have been designed so that the dot product formula is not necessary.

I agree that moving most of C4 vectors to FM was a bit of a strange decision but aside from that I think the increase in difficulty and focus on proof & modelling have been positive overall. They probably had to make a decision to get rid of one of the major topics and it was vectors that got the chop.

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#10

(Original post by

It's strange that on the (Edexcel) spec, students are supposed to learn the formula for finding the angle between a vector and an axis (see textbook pages 340-341) but not the general dot product. Personally, when tutoring, I show them the dot product as it's far easier to understand and apply.

**dextrous63**)It's strange that on the (Edexcel) spec, students are supposed to learn the formula for finding the angle between a vector and an axis (see textbook pages 340-341) but not the general dot product. Personally, when tutoring, I show them the dot product as it's far easier to understand and apply.

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#11

(Original post by

I personally don't think any formula is necessary for that topic. If the student draws the vector then they should be able to see that they can use simple trig to find the angle.

**Sir Cumference**)I personally don't think any formula is necessary for that topic. If the student draws the vector then they should be able to see that they can use simple trig to find the angle.

Dot product is the way to go, and Edexcel was very stupid to remove it. But then we've all seen massive screw-ups by money-grabbing Pearson Publishing. My all time favourite was in their

**own**physics book. Part of a

**large illustration**stated that gluons where made up of quarks: doesn't inspire much confidence.

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#12

(Original post by

A chainsaw isn't necessary for cutting down a tree, but it's a hell of a lot easier than an ax. Your drawing method is probably more time consuming and error prone. Also, the suggested use of arctan is risky as one of the angles returned might be in the wrong quadrant.

Dot product is the way to go, and Edexcel was very stupid to remove it. But then we've all seen massive screw-ups by money-grabbing Pearson Publishing. My all time favourite was in their

**David Getling**)A chainsaw isn't necessary for cutting down a tree, but it's a hell of a lot easier than an ax. Your drawing method is probably more time consuming and error prone. Also, the suggested use of arctan is risky as one of the angles returned might be in the wrong quadrant.

Dot product is the way to go, and Edexcel was very stupid to remove it. But then we've all seen massive screw-ups by money-grabbing Pearson Publishing. My all time favourite was in their

**own**physics book. Part of a**large illustration**stated that gluons where made up of quarks: doesn't inspire much confidence.
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#13

(Original post by

**emma64**)
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#14

(Original post by

I disagree. Finding the angle between a vector and the horizontal/vertical is something that could be in a GCSE exam - there’s no need to learn a formula. I often find that formulas can distract from what’s going on and if the exam asks a different question to what a student is used to from their textbook then they can apply formulas incorrectly without much understanding.

**Sir Cumference**)I disagree. Finding the angle between a vector and the horizontal/vertical is something that could be in a GCSE exam - there’s no need to learn a formula. I often find that formulas can distract from what’s going on and if the exam asks a different question to what a student is used to from their textbook then they can apply formulas incorrectly without much understanding.

**Neither**of the vectors in this question is vertical or horizontal.

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#15

David Getling here is the DFE content for vectors in A Level maths:

As you can see it's very basic now and doesn't go much further than GCSE and it doesn't mention angles at all. I wouldn't be surprised if the question in the OP is from an old spec textbook.

As you can see it's very basic now and doesn't go much further than GCSE and it doesn't mention angles at all. I wouldn't be surprised if the question in the OP is from an old spec textbook.

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#16

(Original post by

David Getling here is the DFE content for vectors in A Level maths:

As you can see it's very basic now and doesn't go much further than GCSE and it doesn't mention angles at all. I wouldn't be surprised if the question in the OP is from an old spec textbook.

**Sir Cumference**)David Getling here is the DFE content for vectors in A Level maths:

As you can see it's very basic now and doesn't go much further than GCSE and it doesn't mention angles at all. I wouldn't be surprised if the question in the OP is from an old spec textbook.

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#17

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(Original post by

Where did you get this question from out of interest? Was it from a new spec textbook?

**Sir Cumference**)Where did you get this question from out of interest? Was it from a new spec textbook?

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