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Mechanics 1 - Dynamics of a Particle Help

I'm having trouble with the following question, I've completed part A, but don't have a clue about part B.



If possible, please tell me how to do it without giving me the answer, I'd prefer to get it on my own. I want to understand why I need to complete certain steps and what it means rather than just knowing the calculations.

Thanks.
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Work out all of the forces on the block both up and down the slope. If there is a resultant the block will accelerate in the direction of the resultant since f=ma

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Is that enough detail or do you want me to elaborate further?

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AlconH
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Original post by samb1234
Is that enough detail or do you want me to elaborate further?

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I think I get it.

Since the block is now going down the slope, the friction is now acting upwards, against the blocks direction of movement, yes?

As a result, I need to subtract the weight component away from the friction to get the resultant force. Since that number will be a positive, the block must be sliding down the slope?
Yes that is correct. One thing to note is that the frictional force is a MAXIMUM so if it asked you to say why a block remained stationary it would be better to write it as Fmax>mgsina therefore the frictional force will equal mgsina so there is no resultant force.

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AlconH
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Original post by samb1234
Yes that is correct. One thing to note is that the frictional force is a MAXIMUM so if it asked you to say why a block remained stationary it would be better to write it as Fmax>mgsina therefore the frictional force will equal mgsina so there is no resultant force.

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Awesome! Thanks. I just did it and got the correct answer. Thank you so much for your help!

Yeah, I know that if the force is less than Fmax, then it cannot move.

Thanks again!
No problem if you have any other issues let me know I'm more than happy to help.

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