Solve Sliding Blocks with Weight 3w & Coefficient of Friction

  • Thread starter Thread starter RoKe
  • Start date Start date
  • Tags Tags
    Blocks Sliding
AI Thread Summary
The discussion revolves around a physics problem involving Block A, which has a weight of 3w, sliding down an inclined plane at a constant speed, while Block B, with weight w, rests on top of it. The analysis includes forces acting on both blocks, considering the components of weight and friction. The net force equation is established to determine the coefficient of kinetic friction, leading to a book answer of 0.450. A participant acknowledges a typo in their angle calculations but confirms that their approach is fundamentally correct. The conversation highlights the importance of careful calculation in solving physics problems.
RoKe
Messages
6
Reaction score
0
Here is the question:
Block A, with weight 3w, slides down an inclined plane S of slope angle 36.9 degrees at a constant speed while plank B, with weight w, rests on top of A and is attached by a cord to the wall. If the coefficient of kinetic friction is the same between A and B and between S and A, determine its value.
Ok, here's what I did:
x is the direction parallel to the slope and y is perpendicular. Forces in the x direction include the component of the weight of Block A (down the slope), the force of friction of S on A and the force of friction of B on A (both resisting the motion down the slope).
I did not include the plank B's weight as part of the force pushing the block down because the component of B's weight parallel to the slope is being countered by the tension in the string (I hope that's right).
The force of friction of S on A is equal to (u_k)4wcos39.9, and the force of friction of B on A is (u_k)wcos39.9.
F_net = 3wsin36.9 - (u_k)4wcos39.9 - (u_k)wcos39.9 = 0 (const. velocity)
The answer in the book is 0.450. I know I'm doing something wrong, but I want to move on to other questions so if someone can help out I'd appreciate it.
 

Attachments

  • IMG.jpg
    IMG.jpg
    2.9 KB · Views: 2,784
Physics news on Phys.org
Except for a typo in your angles (it's 36.9, not 39.9), your analysis is correct and should give you the book's answer.
 
So it does. I guess I was tired and was making mistakes in my calculations. Thanks! :)
 
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

Sliding blocks and a string problem
Replies
1
Views
3K
A-level Maths Mechanics: Prevent Block from Sliding Down Inclined Plane
Replies
30
Views
3K
How friction acts on a block moving down a slope moving side to side
Replies
2
Views
885
Finding the work done by a block
Replies
4
Views
3K
Question Concerning The Coefficient of Friction: Block on a Rough Inclined Plane
Replies
5
Views
2K
Coefficient of kinetic friction of a block sliding across the ceiling
Replies
7
Views
1K
Physics Homework -- block pressed against a wall is sliding....
Replies
4
Views
3K
Sliding resistance of eccentrically loaded block
Replies
20
Views
2K
Friction problem of a block sandwiched between 2 surfaces
Replies
6
Views
1K
Draw a diagram of all the forces acting on block A.
Replies
3
Views
6K

Hot Threads

Recent Insights

Back
Top