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Isaac Physics 'Sliding Blocks' Problem

https://isaacphysics.org/questions/ft_mechanics_core_4?board=y12ms2020_21_week05

Part D. Please, someone, what is the resultant force F.
Reply 1
The coefficient of friction between the lower block and the table hasn't changed since part A. The total weight is also the same as in part A. This means that the friction is still enough to stop the lower block from moving, and its acceleration is zero.
Reply 2
Original post by Zuvio
The coefficient of friction between the lower block and the table hasn't changed since part A. The total weight is also the same as in part A. This means that the friction is still enough to stop the lower block from moving, and its acceleration is zero.

Oh okay I understand what you mean, however I thought that the friction between the two blocks (that there wasn't in the earlier parts) had an effect on the resultant F so would cause F to not equal 0 for the bottom block anymore? Apologies if my confusion doesn't make much sense.
Reply 3
Original post by domm1
Oh okay I understand what you mean, however I thought that the friction between the two blocks (that there wasn't in the earlier parts) had an effect on the resultant F so would cause F to not equal 0 for the bottom block anymore? Apologies if my confusion doesn't make much sense.

True, it could affect the resultant, but in this case, the friction between the two blocks is much less than between the lower block and the table. (0.65N vs. 8.36N). If the friction between the blocks was greater than 4.36N, the lower block would move.
Reply 4
Original post by Zuvio
True, it could affect the resultant, but in this case, the friction between the two blocks is much less than between the lower block and the table. (0.65N vs. 8.36N). If the friction between the blocks was greater than 4.36N, the lower block would move.

You meant 8.36N, right?

So for the bottom block case, as the friction between the blocks is so minimal in comparison to the friction between the bottom block and table, we can assume that the lesser friction is negligible and can be ignored?
Reply 5
Original post by domm1
You meant 8.36N, right?

So for the bottom block case, as the friction between the blocks is so minimal in comparison to the friction between the bottom block and table, we can assume that the lesser friction is negligible and can be ignored?

No, it would only need to be 4.36N, as there is also the 4N force acting, so I subtracted that.

Also, it's not an assumption in this situation, as we have actually calculated the values for all the forces. you have a 4.65N total driving force working against an 8.36N resistive force, so it doesn't move.
Reply 6
Original post by domm1
https://isaacphysics.org/questions/ft_mechanics_core_4?board=y12ms2020_21_week05

Part D. Please, someone, what is the resultant force F.


Hi, could you please tell me what the correct answers for Part A, B, C and D are? and if you have Slipping block could you tell me the answers to that aswell?|

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