Finding work done by friction on a box

AI Thread Summary
To find the work done by friction on a box being pushed across a rough surface, the applied force of friction is calculated using the coefficient of kinetic friction and the normal force. The normal force is affected by the vertical component of the applied force, which is directed at an angle below the horizontal. The initial calculation of frictional force was determined to be 57.82 N, leading to an incorrect work done value of -4156.108 J. The error lies in not properly accounting for the normal force, which is greater than the weight due to the vertical component of the applied force. Accurate resolution of all force components is crucial for determining the correct work done by friction.
99gray
Messages
1
Reaction score
0
1.
A box of mass
m = 59.0 kg
(initially at rest) is pushed a distance
d = 83.0 m
across a rough warehouse floor by an applied force of
FA = 204 N
directed at an angle of 30.0° below the horizontal. The coefficient of kinetic friction between the floor and the box is 0.100. Determine the work done by the force of friction
7-p-001.gif


Homework Equations


W = fdcosΘ
Fƒ=μN

The Attempt at a Solution


I used the two above equations and I found that the applied force of friction would be 57.82 because that is .1*59*9.8 and then if you put that into the first equation, the work would be 57.82*83*cos30 which equals 4156.108 and then since it is opposite the applied force, it would be -4156.108. At least I thought. That's wrong and I don't know why. Please help!
 
Physics news on Phys.org
But in this problem, the normal force is larger than the weight.
 
  • Like
Likes SammyS
The vertical component of F add to weight.
Remember when resolving vector, here force, noted all the components. Here the X and Y components.
 
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Thread 'A cylinder connected to a hanged 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