# MechanicsWatch

Thread starter 7 months ago
#1
Hi, please can i have some help with this question:*https://scontent.fbhx2-1.fna.fbcdn.n...58&oe=5CAA49F6

I get this answer (4m):*https://cdn.discordapp.com/attachmen...24/unknown.png

The answer given in the video was just 2m. Am i wrong, or is the video?
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7 months ago
#2
(Original post by Al4stair)
Hi, please can i have some help with this question:*https://scontent.fbhx2-1.fna.fbcdn.n...58&oe=5CAA49F6

I get this answer (4m):*https://cdn.discordapp.com/attachmen...24/unknown.png

The answer given in the video was just 2m. Am i wrong, or is the video?
2 metres looks good.
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Thread starter 7 months ago
#3
(Original post by RDKGames)
2 metres looks good.
But it says from the point O which is at 6m. Don't you need to minus the 2m from the 6m, which is 4m?
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7 months ago
#4
(Original post by Al4stair)
But it says from the point O which is at 6m. Don't you need to minus the 2m from the 6m, which is 4m?
Don't understand your reasoning.

tells us the displacement of the particle from O, therefore the answer of 2 means the particle is 2m in the positive direction ahead from O. Meaning it's 2 metres from O.
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Thread starter 7 months ago
#5
(Original post by RDKGames)
Don't understand your reasoning.

tells us the displacement of the particle from O, therefore the answer of 2 means the particle is 2m in the positive direction ahead from O. Meaning it's 2 metres from O.
I do not think so, s=t^3 -7t^2 +8t +6 so when t=0, s=6m. The question asks for the distance from O. If you sub t=2 into the equation you get 2m. Now as I have just shown, O is at 6m. So 6m-2m is 4m. S cannot tell us displacement of the particle from O.
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7 months ago
#6
(Original post by Al4stair)
I do not think so, s=t^3 -7t^2 +8t +6 so when t=0, s=6m. The question asks for the distance from O. If you sub t=2 into the equation you get 2m. Now as I have just shown, O is at 6m. So 6m-2m is 4m. S cannot tell us displacement of the particle from O.
I think I can see what you're saying.

The issue here now lies with the fact that the wording of the question is off. Usually this type of question would read "A particle moves in relation to a fixed point O" (which is typicall notation for the origin of the system) which is when the answer of 2m would make sense, and the video you're referring to has interpreted the question as to mean this.

However if we take O to not be the 'origin' as it usually referred to, and we measure from the origin then the point O would be 6m ahead of the origin. Indeed, then we would then have that the distance from O is 4m.

The equation would in either case tell us the displacement of the particle from the origin.
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7 months ago
#7
The way I have interpreted this question is when T=0 the particle is 6m away from point O
When t=2 the particle is 2m away from O
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Thread starter 7 months ago
#8
(Original post by RDKGames)
I think I can see what you're saying.

The issue here now lies with the fact that the wording of the question is off. Usually this type of question would read "A particle moves in relation to a fixed point O" (which is typicall notation for the origin of the system) which is when the answer of 2m would make sense, and the video you're referring to has interpreted the question as to mean this.

However if we take O to not be the 'origin' as it usually referred to, and we measure from the origin then the point O would be 6m ahead of the origin. Indeed, then we would then have that the distance from O is 4m.

The equation would in either case tell us the displacement of the particle from the origin.
I am confused by what you mean, the particle has moved 4m in relation to the fixed point O, surely. Not sure how that would change the question.
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7 months ago
#9
(Original post by Al4stair)
I am confused by what you mean, the particle has moved 4m in relation to the fixed point O, surely. Not sure how that would change the question.
It would change the question because O would then be the origin and the particle wouldn't be starting on it!
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Thread starter 7 months ago
#10
(Original post by RDKGames)
It would change the question because O would then be the origin and the particle wouldn't be starting on it!
The origin would be at 6m. I don't think replacing O with origin would make a difference.
Last edited by Al4stair; 7 months ago
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