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Exuro89
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Homework Statement
There is an 8 kg block on a table with a 6 kg block hanging off of a pulley on the end of a table. The rope and pulley have negligible mass, and the pulley is frictionless. The coefficient of kinetic friction between the 8.00-kg block and the tabletop is 0.250 The blocks are released from rest.
Use energy methods to calculate the speed of the 6.00-kg block after it has descended 1.50 m.
Homework Equations
f=ma
KE=1/2mv^2
The Attempt at a Solution
My problem with this is all of the solutions I've seen use gravitational potential energy, however we haven't gotten to that chapter yet so I can't use it. How else would I solve for it? I know that the net force on the block is 58.8N from finding the smaller blocks force and subtracting the friction force from that.
Old problem
Homework Statement
A physics professor is pushed up a ramp inclined upward at θ=30.0º above the horizontal as he sits in his desk chair that slides on frictionless rollers. The combined mass of the professor and chair is m=85 kg. He is pushed S=2.50 m along the incline by a group of students who together exert a constant horizontal force of F=600 N. The professor’s speed at the bottom of the ramp is = 2.00 m/s. Using energy considerations, find the speed at the top of the ramp.
Homework Equations
W=K_2-K_1
F=ma
W=F*s
The Attempt at a Solution
First thing I did was find the net force on the box. The force of gravity along the displacement would be -mgsin(30) which is -416.5N. Combined with the positive 600N of constant force pushed on the chair we get a net force of 183.5N
Then I multiplied the force by the displacement to get 458.75J
Now I use the work-energy theorum to solve for velocity.
1/2mv_2^2 = 1/2mv_1^2 + Work_tot
1/2*85*v_2^2 = 1/2*85*2^2 + 458.75
v = 3.85m/s
I looked online to see if I could compare my answers with someone else and I found this site that has the same question, but it has a different answer and I'm not sure why mine doesn't match. http://www.hostos.cuny.edu/departments/math/MTRJ/archives/volume4/problemsolving/2.%20presentation.problem-solving.article.yr.pdf
Is there something I'm overlooking in the problem?
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