Finding friction - block attached to ball

AI Thread Summary
If a problem does not provide a coefficient of friction, it is generally assumed that the surface is frictionless for calculations. In the discussed scenario, the block is attached to a 100N weight over a pulley, and the distance it moves in 3 seconds can be determined under this assumption. However, if the problem later asks for the minimum coefficient of friction to prevent movement, it indicates that friction must be considered for that part. The lack of explicit mention of friction in the problem suggests that the first part should be solved as if there is no friction, while the second part requires calculating friction. Overall, clarity in problem statements regarding friction is essential for accurate solutions.
Kaxa2000
Messages
71
Reaction score
0
If the problem doesn't give a coefficient of friction does that mean you solve it without the friction? Do you solve for friction somehow? I'm supposed to find the distance a block moves in 3 secs that's attached to a 100N weight over a pulley. Block is on flat surface...no friction coefficient is given...do I solve it on a frictionless surface?
 
Physics news on Phys.org
If they don't give you any information about friction, I would just assume that the surface is frictionless.

But post the exact problem, word-for-word, if you are unsure.
 
Kaxa2000 said:
If the problem doesn't give a coefficient of friction does that mean you solve it without the friction? Do you solve for friction somehow? I'm supposed to find the distance a block moves in 3 secs that's attached to a 100N weight over a pulley. Block is on flat surface...no friction coefficient is given...do I solve it on a frictionless surface?

Hi Kaxa2000! :smile:

Sounds like a bad question. :frown:

The question should always say "frictionless" if that's intended (or some other code-word, like "smooth", or "ice", which is always assumed to be frictionless!).

If no friction coefficient is given, I don't see how you can solve this (unless, for example, the block is a cylinder and it's rolling, in which case the coefficient wouldn't matter).
 
It doesn't mention frictionless, but the reason why I wonder if there's a way to solve for kinetic friction is because at the end of the problem it asks what minimum coefficient of friction is required to keep the block from moving.

Is it possible to do that on a frictionless surface?? I got 1.0 for the coefficient of static ...does that seem right?
 
I assume that for the first part, you assume that it's frictionless, and for the second part, you assume that it isn't.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Finding the work done by a block
Replies
4
Views
3K
Two bars connected by a spring on a floor with friction
Replies
37
Views
1K
Newton's law problem: Pushing 2 stacked blocks on a horizontal table
Replies
13
Views
3K
Distance traveled by a Ball affected by friction after t seconds
Replies
4
Views
2K
Newton's Second Law (Pulley Sustem)
Replies
3
Views
2K
Friction force on a ball falling through a body of water
Replies
9
Views
1K
Two block problems with friction
Replies
6
Views
2K
When Friction the block m2 start to move?
Replies
11
Views
2K
Friction Required for Billiard Ball to Roll without Slipping
2
Replies
60
Views
4K
Finding acceleration of block with block on top, connected by rope
Replies
6
Views
2K

Hot Threads

Recent Insights

Back
Top