coconut64
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Name:  1457977331272-1542586955.jpg
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Size:  383.9 KBfor this question when asked to find deceleration, why does friction and the other force act in the same direction? I thought friction opposes the downward force ?? Attachment 512877512879 thanks.
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Zacken
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(Original post by coconut64)
Name:  1457977331272-1542586955.jpg
Views: 133
Size:  383.9 KBfor this question when asked to find deceleration, why does friction and the other force act in the same direction? I thought friction opposes the downward force ?? Attachment 512877512879 thanks.
The motion is up the plane, so the friction opposes motion and acts down the plane.
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coconut64
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(Original post by Zacken)
The motion is up the plane, so the friction opposes motion and acts down the plane.
But at first the direction of acceleration is unknown though. The weight is acting downward so why isn't friction opposing the force acting downward?
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B_9710
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(Original post by coconut64)
But at first the direction of acceleration is unknown though. The weight is acting downward so why isn't friction opposing the force acting downward?
Direction of acceleration is irrelevant. Friction opposes motion and so acts in the opposite direction to the direction in which an object is travelling.
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Zacken
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(Original post by coconut64)
But at first the direction of acceleration is unknown though. The weight is acting downward so why isn't friction opposing the force acting downward?
Friction opposes motion. The particle is moving up the plane; hence the motion is up the plane; hence friction is down the plane; acceleration is utterly irrelevant.
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coconut64
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(Original post by Zacken)
Friction opposes motion. The particle is moving up the plane; hence the motion is up the plane; hence friction is down the plane; acceleration is utterly irrelevant.
Okay.. but I was not told that there is any force acting upward. So you determine the direction of the friction solely on the word 'up' the plane?
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Zacken
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(Original post by coconut64)
Okay.. but I was not told that there is any force acting upward. So you determine the direction of the friction solely on the word 'up' the plane?
Yes. This will be the case for every M1 question. Either a particle is projected upwards or downward (to the plane). You should then be able to draw your friction right away.
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coconut64
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(Original post by B_9710)
Direction of acceleration is irrelevant. Friction opposes motion and so acts in the opposite direction to the direction in which an object is travelling.
But it isn't mometiomed in the question what force acts up the plane though. Thanks
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drandy76
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(Original post by coconut64)
But it isn't mometiomed in the question what force acts up the plane though. Thanks
It's movement comes from th initial projection from the machine, on,y forces acting upon it are the contact forces and its own weight


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coconut64
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#10
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(Original post by Zacken)
Yes. This will be the case for every M1 question. Either a particle is projected upwards or downward (to the plane). You should then be able to draw your friction right away.
Are you sure?? Because in the question I can only see the weight acting downward and that's the only force. But your explanation makes sense...
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Zacken
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(Original post by coconut64)
Are you sure?? Because in the question I can only see the weight acting downward and that's the only force.
Yes. I am sure. The question clearly says, in the first paragraph, that the ball is fired up the plane. So the motion is upwards!!!!! Hence the friction opposes motion.
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Marxist
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(Original post by Zacken)
The motion is up the plane, so the friction opposes motion and acts down the plane.
Hi Zain,

Is it okay for me to post a full solution?
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coconut64
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(Original post by Zacken)
Yes. I am sure. The question clearly says, in the first paragraph, that the ball is fired up the plane. So the motion is upwards!!!!! Hence the friction opposes motion.
Oh okay. I didn't realise that. Thank you for helping
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(Original post by Zacken)
Yes. I am sure. The question clearly says, in the first paragraph, that the ball is fired up the plane. So the motion is upwards!!!!! Hence the friction opposes motion.
Oops, not allowed.
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Zacken
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(Original post by Marxist)
Oops, not allowed.
What d'you mean?
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Marxist
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(Original post by Zacken)
What d'you mean?
Soz, I meant - I'm not allowed to post a full solution.
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Notnek
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(Original post by Marxist)
Hi Zain,

Is it okay for me to post a full solution?
Are you an M1 student? You can post a solution in a spoiler if you want us to check.

The OP doesn't seem to need help with the question so posting a full solution for them would be a waste of time, and against the rules
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coconut64
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#18
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(Original post by notnek)
Are you an M1 student? You can post a solution in a spoiler if you want us to check.

The OP doesn't seem to need help with the question so posting a full solution for them would be a waste of time, and against the rules
Yes i am. I get it now so it is not unnessary to post a full solution but thanks for helping anyway. I appreciate it.
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