# Alevel maths help on mechanics question

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https://imgur.com/gallery/iPmI7AS

How do I do this question?

For part a I differentiated v to get acceleration, set this equal to 0 and get t as 0.75 seconds

For part b I set v equal to 0 and get t is 3.5 seconds and then integrated v and subbed in t is 3.5 into this to get -38.79 m is this correct? If not could someone please give some pointers

How do I do this question?

For part a I differentiated v to get acceleration, set this equal to 0 and get t as 0.75 seconds

For part b I set v equal to 0 and get t is 3.5 seconds and then integrated v and subbed in t is 3.5 into this to get -38.79 m is this correct? If not could someone please give some pointers

Last edited by iqraali2002; 1 month ago

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#2

(Original post by

https://imgur.com/gallery/iPmI7AS

How do I do this question?

For part a I differentiated v to get acceleration, set this equal to 0 and get t as 0.75 seconds

For part b I set v equal to 0 and get t is 3.5 seconds and then integrated v and subbed in t is 3.5 into this to get -38.79 m is this correct? If not could someone please give some pointers

**iqraali2002**)https://imgur.com/gallery/iPmI7AS

How do I do this question?

For part a I differentiated v to get acceleration, set this equal to 0 and get t as 0.75 seconds

For part b I set v equal to 0 and get t is 3.5 seconds and then integrated v and subbed in t is 3.5 into this to get -38.79 m is this correct? If not could someone please give some pointers

Last edited by mqb2766; 1 month ago

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(Original post by

Integrating v from t=0 to 3.5 should be ok. However velocity is +ive in this region, so your distance/displacement should be +ive? Upload what youve done?

**mqb2766**)Integrating v from t=0 to 3.5 should be ok. However velocity is +ive in this region, so your distance/displacement should be +ive? Upload what youve done?

This is my working out. Could u check part a and b please?

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#4

(Original post by

https://imgur.com/gallery/DAYHqVx

This is my working out. Could u check part a and b please?

**iqraali2002**)https://imgur.com/gallery/DAYHqVx

This is my working out. Could u check part a and b please?

Also, it would be better to write the definite integral to make the limits clear. If you do an indefinite, you need to include the integration constant.

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(Original post by

Seems roughly ok, but do you know why you get a negative displacement for b)?

Also, it would be better to write the definite integral to make the limits clear. If you do an indefinite, you need to include the integration constant.

**mqb2766**)Seems roughly ok, but do you know why you get a negative displacement for b)?

Also, it would be better to write the definite integral to make the limits clear. If you do an indefinite, you need to include the integration constant.

Last edited by iqraali2002; 1 month ago

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#6

(Original post by

Oh okay thanks. I rewrote it using indefinite integral and get 55.46. I see what I did wrong cuz I just ignored the t is -2 solution. Thanks for your help

**iqraali2002**)Oh okay thanks. I rewrote it using indefinite integral and get 55.46. I see what I did wrong cuz I just ignored the t is -2 solution. Thanks for your help

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(Original post by

Err, I think youve made things worse, so my help wasnt that good ..

**mqb2766**)Err, I think youve made things worse, so my help wasnt that good ..

https://imgur.com/gallery/lYZpauP

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#8

The lower limit should be the obvious one when the "simulation" starts.

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(Original post by

For a definite integral you need ot put the limits on the integral sign, not just bring them in at the end.

The lower limit should be the obvious one when the "simulation" starts.

**mqb2766**)For a definite integral you need ot put the limits on the integral sign, not just bring them in at the end.

The lower limit should be the obvious one when the "simulation" starts.

When P changes direction of motion is when v is 0. When v is 0 the t values are 3.5 and -2.

Then I integrated v to get distance with the parameters 3.5 and -2

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(Original post by

The question tells you it wants the distance between O and P. O is ...

**mqb2766**)The question tells you it wants the distance between O and P. O is ...

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#12

(Original post by

Could u do the question and tel me what u get for the distance of P from O at the instant when P changes its direction of motion. In the question it says point O is on the line but it doesn’t specific whether that O is the origin

**iqraali2002**)Could u do the question and tel me what u get for the distance of P from O at the instant when P changes its direction of motion. In the question it says point O is on the line but it doesn’t specific whether that O is the origin

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(Original post by

Yes it does, at the start. O is the position at time t=0.

**mqb2766**)Yes it does, at the start. O is the position at time t=0.

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#14

(Original post by

Oh my god I’m an actual idiot okay so O is in the origin so do I divide by answer of 55.46 by 2? Or am I doing it completely wrong?

**iqraali2002**)Oh my god I’m an actual idiot okay so O is in the origin so do I divide by answer of 55.46 by 2? Or am I doing it completely wrong?

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(Original post by

You integrate velocity from O to P, which is pretty much what you were doing originally.

**mqb2766**)You integrate velocity from O to P, which is pretty much what you were doing originally.

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#16

(Original post by

And for the upper and lower number on the integral I use 3.5 and 0? To get s is 38.79?

**iqraali2002**)And for the upper and lower number on the integral I use 3.5 and 0? To get s is 38.79?

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(Original post by

Yes.

**mqb2766**)Yes.

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