# Stuck on a mechanics Q

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Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass is which means I can't find out the weight

Any help would be nice. Thanks

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass is which means I can't find out the weight

Any help would be nice. Thanks

Last edited by Yatayyat; 1 year ago

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#2

(Original post by

Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass which means I can't find out the weight

Any help would be nice. Thanks

**Yatayyat**)Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass which means I can't find out the weight

Any help would be nice. Thanks

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(Original post by

What would be the acceleration when the mass is just about heavy enough to cause movement?

**mqb2766**)What would be the acceleration when the mass is just about heavy enough to cause movement?

If tension balances with the frictional force then it could supposedly be moving at a steady speed since the resultant force becomes zero?

So in order for the block to accelerate forward, it must exceed the frictional force there. I know that the frictional force is '0.26 * 0.10g = 0.2548N' equating that to 'ma' where F (force) is 0.2548N, then a = 0.2548/0.10 = 2.548 ms^-2.

So the acceleration must be bigger than 2.548 ms^-2 for the block to cause movement?

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#4

(Original post by

Well the block can only move to the right once the tension on the rope becomes more than or equal to the frictional force pushing it back.

If tension balances with the frictional force then it could supposedly be moving at a steady speed since the resultant force becomes zero?

So in order for the block to accelerate forward, it must exceed the frictional force there. I know that the frictional force is '0.26 * 0.10g = 0.2548N' equating that to 'ma' where F (force) is 0.2548N, then a = 0.2548/0.10 = 2.548 ms^-2.

So the acceleration must be bigger than 2.548 ms^-2 for the block to cause movement?

**Yatayyat**)Well the block can only move to the right once the tension on the rope becomes more than or equal to the frictional force pushing it back.

If tension balances with the frictional force then it could supposedly be moving at a steady speed since the resultant force becomes zero?

So in order for the block to accelerate forward, it must exceed the frictional force there. I know that the frictional force is '0.26 * 0.10g = 0.2548N' equating that to 'ma' where F (force) is 0.2548N, then a = 0.2548/0.10 = 2.548 ms^-2.

So the acceleration must be bigger than 2.548 ms^-2 for the block to cause movement?

So solve for T and m with a=0.

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(Original post by

The acceleration is zero? Increeasing the mass just enough will break the equilibrium.

So solve for T and m with a=0.

**mqb2766**)The acceleration is zero? Increeasing the mass just enough will break the equilibrium.

So solve for T and m with a=0.

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#6

(Original post by

Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass is which means I can't find out the weight

Any help would be nice. Thanks

**Yatayyat**)Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass is which means I can't find out the weight

Any help would be nice. Thanks

Last edited by RogerOxon; 1 year ago

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#7

If the block is light, there is no movement so a=0. Its in equilibrium.

Increasing the mass slowly there will become a critical point where movement is just about to start. Here a=0, but your equations hold.

When the mass in larger than the critical value, the acceleration will be higher.

Increasing the mass slowly there will become a critical point where movement is just about to start. Here a=0, but your equations hold.

When the mass in larger than the critical value, the acceleration will be higher.

Last edited by mqb2766; 1 year ago

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#8

(Original post by

I don't quite get why a= 0 for the block to move?

**Yatayyat**)I don't quite get why a= 0 for the block to move?

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Yes, thank you I can see now why a = 0 here

I have tried subbing in a = 0 and have got around to finding the weight to be 0.2548N

So in actual fact I could have just worked out what the frictional force was to be and know that would be equal to the weight hanging down. As we're only looking for the point where frictional force is overcome like you have said for movement just about to occur.

I have tried subbing in a = 0 and have got around to finding the weight to be 0.2548N

So in actual fact I could have just worked out what the frictional force was to be and know that would be equal to the weight hanging down. As we're only looking for the point where frictional force is overcome like you have said for movement just about to occur.

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#10

(Original post by

Yes, thank you I can see now why a = 0 here

I have tried subbing in a = 0 and have got around to finding the weight to be 0.2548N

So in actual fact I could have just worked out what the frictional force was to be and know that would be equal to the weight hanging down. As we're only looking for the point where frictional force is overcome like you have said for movement just about to occur.

**Yatayyat**)Yes, thank you I can see now why a = 0 here

I have tried subbing in a = 0 and have got around to finding the weight to be 0.2548N

So in actual fact I could have just worked out what the frictional force was to be and know that would be equal to the weight hanging down. As we're only looking for the point where frictional force is overcome like you have said for movement just about to occur.

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#11

**Yatayyat**)

Here is the Q below

I have made an attempt at it, but I'm getting nowhere as I end up getting 2 unknowns at the end therefore I can't solve for what the mass is which means I can't find out the weight

Any help would be nice. Thanks

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reply

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