Find the coefficient of kinetic friction between the crate and the surface

AI Thread Summary
The discussion revolves around calculating the coefficient of kinetic friction for a crate weighing 49 N, which accelerates at 0.5 m/s² when pulled by a 14.5 N force at a 19-degree angle. The user initially struggles with the equations needed to find the normal force and the frictional force, questioning the angle's orientation and the relationship between forces. Key points include recognizing that the net force must account for both horizontal and vertical components of the applied force. Ultimately, the user successfully figures out the solution with assistance from the forum, confirming the coefficient of kinetic friction as 0.253. The conversation highlights the importance of understanding force components and the relationship between friction and normal force in physics problems.
hannsparks
Messages
31
Reaction score
0
Coefficient of kinetic friction

I have a mojor physics test thursday (two days) and here is a pretest question that I cannot figure out if anyone can figure it out I'd greatly appreciate it. I actually know what the answer is uk=0.253 I just don't know how to get that answer.
" An apple crate with a weight of 49 N accelerates at a rate of 0.5 m/s2 along a horizontal surface as the crate is pulled with a force of 14.5 N as shown in Figure 1. The angle at which the crate is being pulled is 19 degrees.
Find the coefficient of kinetic friction between the crate and the surface."

heres my attempt: N=49+Fsin19 y direction
Fcos19-uk=(5)(0.5) x direction
I then tried to combine the two equations to figure out N and F but I am stuck.
 
Last edited:
Physics news on Phys.org
First of all is the angle 19, the angle over the horizontal or under? If it is over then you have to write that N=49-Fsin19 . Also, uk isn't a force, N*uk is the force of friction.
 
Draw a picture and label the forces.

If the create is accelerating there must be a net force (F = m*a).
You know that a 14.5 N force is being exerted on the box at 19 degrees. What part of this 14.5 N is going to accelerate the box horizontally? What part tries to accelerate it vertically?

Remember,
The force of friction = coefficient of friction * normal force.
The force of friction points in the opposite direction of motion.
 
im so confused I have no idea what to do next.. do I know have to combine the two equations to figure out N and F?
 
hey guess what..I figured it out! Thanks for all your help :)
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top