- #26

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i honestly don't see the difficulty … surely the question will tell you whether to add or subtract?

(almost always you add: in this question, the 3000 N is forwards, and the 4000 N is backwards: when you add them, you get 1000 N backwards)

can you give an example of a question where you've been confused?

you split them into components by multiplying by cosθ or sinθ

you should really use (scosθ, ssinθ),

but cosθ is so close to 1 that you may as well call it 1

that's correct … the work done by gravity is minus 600 J per metre of displacement

no

(why are you using 60,000 ? )

the 4000 and the 3000 are inexactlythe same direction as the displacements,so you don't need to split anything into components, do you?

Hi chet,

I had posted a threat not so long ago with similar friction problems but never understood the help given, i wanted information to help my understanding to solve friction problems generally in a variety of situations. This was the thread, take a look:

https://www.physicsforums.com/showthread.php?t=718970

I managed to solve the questions by getting help from here and there but my understanding of the physics is still weak, understanding this physics and then knowing what formula to use automatically having read the situation correctly which i find most challenging.

In regards to using scosθ, ssinθ, is the s the distance/displacement? and are scosθ and ssinθ forces as a whole acting on the train? if so how can one know what direction they act on the train? i assume the sin is the horizontal along the ramp? and the cos component vertical acting downwards which would be mg while the sin component would be the net force?

Since you say 4,000 and 3,000 in same direction then it would be (1,000) (1, 0.01) is that correct?