
#1
Feb2611, 06:31 AM

P: 4

1. The problem statement, all variables and given/known data
Would constant velocity down a slope be achieved by a cart, by having the frictional force equal to that of Wsinθ (Where W is the weight force and θ is the angle between the slope and the horizontal). 2. Relevant equations/3. The attempt at a solution For example if θ was equal to 15 and W was equal to 19. Then to achieve a constant velocity the frictional force would need to equal approximately 4.92 N. Or am I going in the wrong direction with this? Any help is appreciated and please excuse any ambiguity within this post. 



#2
Feb2611, 07:57 AM

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hi phy124! welcome to pf!
good ol' Newton's second law in that direction means that ∑F = 0, so friction = Wsinθ … what is worrying you about that? 



#3
Feb2711, 12:26 AM

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#4
Feb2711, 03:01 AM

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Constant velocity down a slope
hi phy124!
(just got up …) yes, if there's wheels and no brakes, then the friction with the ground is irrelevant (there is no work done ) … the only thing slowing the cart is friction in the bearings (between the wheel and the axle), and air resistance … usually not enough to overcome gravity and keep a constant velocity! (actually you're wrong about the direction of friction from the ground … for driving or braking wheels, attached to the engine, the friction is in the same direction as the acceleration or braking, but for nondriving nonbraking wheels, surprisingly it's in the opposite direction! ) 



#5
Feb2711, 04:40 AM

P: 8

Hi,
The cart is given three forces: gravity(W), support force(N) and frictional resisntance(F). If the cart is moving with constant velocity along the slope, the force along the slope should be zero, which means Wsinθ = F. As for dynamic frictional resistance, we have the equation F= Nμ, where μ is friction coefficient. Another equation we have is N = Wcosθ. So the final equation to satify your requirement is tanθ = μ. Without information about the friction coefficient, we could get the answer. 



#6
Feb2711, 04:51 AM

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hi 9une! welcome to pf!




#7
Feb2711, 04:57 AM

P: 8

no, as phy124 points out, µ is irrelevant if the cart has wheels and no brakes [/QUOTE]
In my opinion, µ is decided by wheels and brakes. How could we say µ is irrelevant? 



#9
Feb2711, 10:55 PM

P: 4




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