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October 21, 2025, 04:46:11 am
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Author Topic: Neap Motion Question  (Read 2448 times)  Share 

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Shark 774

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Neap Motion Question
« on: June 05, 2011, 04:41:42 pm »
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For the attached question I took the term "reaction force" to mean the total force of the road on the car, but the solutions took it to mean just the normal force, i.e. the force that acts perpendicular to the road. So for my answer I got (using pythagoras' theorem) F ^ 2 = (20,000sin(20) + 500)^2 + (12,000cos(20))^2 and therefore F = 13,455N.

What do you guys think the proper meaning of "reaction force" should be?

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« Last Edit: June 05, 2011, 04:43:45 pm by Shark 774 »
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xZero

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Re: Neap Motion Question
« Reply #1 on: June 05, 2011, 04:49:32 pm »
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I always take reaction force as the normal force, hence friction shouldn't be apart of it

Also the question is worth 2 marks, what you did there is probably worth ~4 marks
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DisaFear

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Re: Neap Motion Question
« Reply #2 on: June 05, 2011, 05:02:03 pm »
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Is the question asking for the normal force? I am feeling confused now, because my answer doesn't match yours :(
Yours is correct right?
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GuessWho

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Re: Neap Motion Question
« Reply #3 on: June 05, 2011, 05:06:31 pm »
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Whenever I read reaction force my brain instantly jumps to the normal force. Probably because my teachers always taught us by it calling normal reaction force.
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Shark 774

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Re: Neap Motion Question
« Reply #4 on: June 05, 2011, 05:14:14 pm »
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Quote from: DisaFear on June 05, 2011, 05:02:03 pm
Is the question asking for the normal force? I am feeling confused now, because my answer doesn't match yours :(
Yours is correct right?

My answer is incorrect according to the neap answers. It's just a matter of what you take "reaction force" to mean. I still feel confident that in this situation "reaction force" is the total force by the road on the car, but just opinion. The question should've been clearer I reckon!
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DisaFear

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Re: Neap Motion Question
« Reply #5 on: June 05, 2011, 05:15:04 pm »
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What is the answer then, if you don't mind? :)
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b^3

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Re: Neap Motion Question
« Reply #6 on: June 05, 2011, 05:37:32 pm »
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ok isn't the force that the road is applying away from the road, that is it is perpendicular to the slope and the other force that you are using, is parallel to the slope and is a component of the force of gravity and not that the road is applying? So the reation force is just the force away from the road. correct me if I am wrong but is this way of thinking correct?
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Shark 774

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Re: Neap Motion Question
« Reply #7 on: June 05, 2011, 06:54:21 pm »
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Quote from: b^3 on June 05, 2011, 05:37:32 pm
ok isn't the force that the road is applying away from the road, that is it is perpendicular to the slope and the other force that you are using, is parallel to the slope and is a component of the force of gravity and not that the road is applying? So the reation force is just the force away from the road. correct me if I am wrong but is this way of thinking correct?

Nah, the road is applying the normal force, perpendicular to the road and a force perpendicular to the road, up the slope (this is the force that opposes gravity and friction and keeps the car at a constant velocity).

The answer given was 11000N
« Last Edit: June 05, 2011, 08:13:13 pm by Shark 774 »
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DisaFear

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Re: Neap Motion Question
« Reply #8 on: June 05, 2011, 06:55:45 pm »
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What was the given answer?
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Lasercookie

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Re: Neap Motion Question
« Reply #9 on: June 05, 2011, 07:04:35 pm »
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I took the reaction force as the normal force.

N = mg cos theta

N = 1200 * 10 * cos 20
N = 11276
N = 11000
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DisaFear

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Re: Neap Motion Question
« Reply #10 on: June 05, 2011, 07:05:51 pm »
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Shouldn't mg = ~12000N?
The mass is 1200kg

And just curious, why is the angle 30?

EDIT: been fixed
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Re: Neap Motion Question
« Reply #11 on: June 05, 2011, 07:06:30 pm »
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Quote from: DisaFear on June 05, 2011, 07:05:51 pm
And just curious, why is the angle 30?

Made a mistake while typing it out.
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RobM8

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Re: Neap Motion Question
« Reply #12 on: June 05, 2011, 07:39:07 pm »
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Reaction force is always the normal force? Last year I never came across a question where they referred to reaction force to be anything else.
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Shark 774

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Re: Neap Motion Question
« Reply #13 on: June 05, 2011, 08:14:46 pm »
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Quote from: DisaFear on June 05, 2011, 07:05:51 pm
Shouldn't mg = ~12000N?
The mass is 1200kg

And just curious, why is the angle 30?

EDIT: been fixed

The mass of the whole thing is 1200kg but to find the normal reaction on just the car you take the mass of the car.
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Lasercookie

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Re: Neap Motion Question
« Reply #14 on: June 05, 2011, 08:22:45 pm »
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The mass of the whole thing would be 1200 + 800 = 2000kg
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