Mechanics Friction Coefficient Question

In this Question, how can I calculate R ? R will be negative as the vertical component caused by the 42N will be greater than the weight alone, so R would have to be negative to counter this, yet R is a force so must be positive, right ?



What do I do ?

Thanks.

In this Question, how can I calculate R ? R will be negative as the vertical component caused by the 42N will be greater than the weight alone, so R would have to be negative to counter this, yet R is a force so must be positive, right ?



What do I do ?

Thanks.

Not quite sure what you're thinking here!

The 42N force has a vertical component that must match the weight, otherwise the particle would take off. That gives you the frictional force via F = (mu)R.

Then you can resolve horizontally to get the net horizontal force and hence acceleration.

But what about R ? The vertical component is not the same as R;

W = R + Y , where Y is the vertical component of the 42N force.

But what about R ? The vertical component is not the same as R;

W = R + Y , where Y is the vertical component of the 42N force.

But what about R ? The vertical component is not the same as R;

W = R + Y , where Y is the vertical component of the 42N force.

BTW is this a question from a textbook or just an online test somewhere?

This is from Dr Frost.

Oh right. Somebody wasn't paying attention when they set the question

Think your equations are mixed up.
The force of 15 prevents sliding down the slope so calculate mu.
Then flip friction and calculate force about to push the block up the slope.
F=15 in the first scenario and is the balancing force for weight and friction.

Bad question. Move on to next one. R cannot be negative.